Multiple Group One-winning rider Pat Smullen has announced his retirement from the saddle.
Smullen, 41, was diagnosed with pancreatic cancer in March last year and has been undergoing treatment.
While his progress remains positive, he said in his weekly column for thoroughbreddailynews.com: "I have had a frank discussion with my doctors and I gave them the full details of the way of life of a jockey, and what I'd have to go through to get back to full fitness, to get back to the weight that I need to be, and to compete at the level I want to compete at.
"They advised me that I should not compromise my immune system in any way. So, taking that into account, the right thing for me to do is to call it a day.
"I've been very fortunate through my career to meet some great people and to ride some very good horses.
"I have a lot of cherished memories of a great career, and I'm very thankful for that. Now it's the second chapter of my life. I think everyone has gathered by now that horses are everything in my life.
"I know nothing else and I'm determined that I'll still work within the industry and, hopefully, I can be of some benefit."
Expanding on his successful recovery, Smullen said: "I don't want to make a huge deal of it, but it's been a tough year and it has taken its toll on my body.
"I had two surgeries and when I recovered from that I had to then face another round of chemotherapy treatment. It was tough going, but it has all been worthwhile and thankfully it has gone very well.
"Whatever has gone in the past in my career, and I like to think I achieved a little bit, this was the biggest achievement of all, getting through this, and I definitely now see life from a different perspective.
"I can never be thankful enough to the medical people who have given me a second chance at life."
Frankie Dettori hailed Smullen an "absolute professional". Dettori shared the weighing room with Smullen for over two decades and was fulsome in his praise of both the rider and the man.
He said: "I've known Pat for 25 years and I've travelled the world with him. He is a great man in every way - a true gentleman.
"He is 100 per cent professional and was a great rider. He won almost everything there is to win, including the Epsom Derby.
"He has won the biggest battle of them all at the moment and I'm sure I will keep in touch with him, as he is a great friend and we will miss him as a rider. It takes a man of great courage and bravery to go through what he has gone through."
He added: "He had everything as a rider. He had a good tactical brain and was very strong and polished. He did everything correctly and didn't do anything dirty, he was just an absolute professional.
"He never got upset or started shouting at people - he was well polished as a person."
Dettori pointed to Smullen's Epsom success on the Dermot Weld-trained and Aga Khan-owned Harzand as a standout moment.
He said: "It is everybody's dream to win the Derby - to win it for the Aga Khan must have been pretty special and that is the ride that stands out for me. He has won nine champion jockey titles, which is also amazing.
"As a friend I'm pleased he is still with us, as a year ago things didn't look great and when you have known someone for so long you are scared for them. He didn't stop (riding) on his one terms, but at least he is still with us.
"Pat put me on my ride in the Derby last year (Hazapour) and I've been keeping close tabs and seeing how he has been doing.
"He has been through all sorts and while we all wanted him back as a rider, if the doctors are saying he can't then he has made the right decision.
"He had big boots to fill in Michael Kinane's, but he did fill those boots and I'm sure Michael is proud of what he has done.
"I can see him moving into a managerial role for one of the big owners he has ridden for, as he is a complete all-round professional who knows the game inside out."
Fran Berry, who himself was forced into retirement earlier this year, was also among those to lead the tributes.
Berry told sportinglife.com: "I've known Pat from day one when it comes to my riding days and we've gradually become very good friends. Myself, Pat, Declan McDonogh and a few others have been really close for years and he's a great man.
"He's been a fantastic rider throughout his career but the last year has really been the measure of the man.
"Thankfully he's come out the right side of that after the cancer diagnosis and while it's sad that he's retiring from riding, he's got the whole rest of his life ahead of him.
"In terms of his quality in the saddle, he's right up there with the likes of Mick Kinane and Johnny Murtagh as top Irish riders, he's an ultra professional and it made no difference whether it was Ballinrobe on a Tuesday or the Curragh on a big Saturday.
"He was particularly good from the front - you never liked to see him making the running if you'd missed the break and were near the back.
"We used to travel together to the course and talk tactics and then try and knock each other off the track and beat each other in the heat of the battle but we'd always have a laugh about it afterwards. Those were some of the fondest moments of my career so I've mixed emotions, obviously.
"As for his highlights, Free Eagle - when he beat the Grey Gatsby at Ascot - was a tremendous ride. A tactical masterclass, while the Derby was a crowning moment. It was Dermot Weld's first winner of the race and Harzand going on to win the Irish Derby was superb - the highlight of a fantastic career."
Champion jockey in Ireland nine times, Smullen has long been associated with Dermot Weld, enjoying success on a global scale with the master of Rosewell House.
Derby glory at Epsom came their way in 2016 with Harzand, who followed up in the Irish Derby at the Curragh - a race the pair also won with Grey Swallow in 2004.
Refuse To Bend was Smullen's first British Classic winner when lifting the 2000 Guineas at Newmarket in 2003. Like Free Eagle, another star for Weld and Smullen, Refuse To Bend raced in the famous silks of Moyglare Stud.
Moyglare's breeding advisor, Fiona Craig, said: "What a star Pat has been and still is. I think this news has been coming for a while and I know Pat is happy and comfortable with it now.
"I'm sure he'd have liked to go out on his own terms and gone out with a Group One winner like Ruby (Walsh) did last week, but he's alive and that's the main thing after what he's been through.
"Pat has ridden for Moyglare for over 20 years and his first Group-race success for the stud was on board Token Gesture in the C.L.Weld Park Stakes at the Curragh in 1996. I remember we had two in the race, with Mick Kinane on Absolute Glee, but it was Pat who came out on top that day.
"Moyglare have only had two retained jockeys in Mick and Pat and he has been a great friend and a great jockey.
"He'll always be a huge part of Moyglare. He's ridden most of our mares and most of their offspring and he's a great sounding board.
"We've had some great days together with the likes of Free Eagle winning at Royal Ascot and Irresistible Jewel and Irresistible Jewel's daughter Princess Highway.
"We've had some great times and I'm sure Pat will continue to ride out as he moves into the next chapter in his life."
More reaction from the racing world...
Mick Kinane, 13-times Irish champion Flat jockey
"Pat has come through a tough time and it's good to see he's got his health back, which is obviously the main thing.
"He's been a very good jockey and can be very proud of the career he's had.
"We had some good scraps and some great times, on and off the track. Hopefully they'll continue."
Aidan O'Brien, multiple champion trainer
"Pat was second to none, both as a jockey and a horseman. As a human being he has inspired people all over the world, especially with the way he has dealt with and spoken about his illness.
"We, like everybody else, look forward to reading his articles and hearing his interviews as his knowledge, experience and wisdom will be an invaluable contribution to everyone."
Joseph O'Brien, dual Irish champion Flat jockey
"Pat is someone I looked up to both before I started riding and after I started riding - he was an idol of mine.
"I was lucky enough to be able to ride against him for a number of years. We were tough competitors, but he was always an absolute gentleman and we had some great times together on and off the track.
"He's a great man and a great jockey and I wish him all the best in whichever road he chooses to go down in the future."
Kevin O'Ryan, Smullen's agent and brother-in-law
"I first met Pat when we were both working in Dermot Weld's and he gave me the opening I was looking for when he asked me to be his agent.
"He's now my brother-in-law and a great friend.
"For me, Pat Smullen epitomises the word professionalism - he's got an unbelievable work ethic and determination and he's someone all young jockeys should aspire to.
"It really is the end of an era with Pat and Ruby (Walsh) retiring in the last week, but as one chapter closes another one opens and I'm sure Pat will go on to be a huge success in whatever he decides to do going forward."
Declan McDonogh, former Irish champion Flat jockey
"We've become very close over the years - I'm actually godfather to one of Pat's sons, Paddy.
"It's been an emotional rollercoaster over the last year or so and it's great that he's got over that big hurdle now, which is the main thing.
"Career-wise he's had a fantastic time. We had plenty of battles on the track and he's been a phenomenal jockey, a brilliant professional and a fantastic role model for any young jockeys coming through.
"I started three or four years after Pat and we've soldiered on together. It's a bit surreal now that he's retired and Fran Berry has recently retired as well - the older crew is getting smaller!
"It's unbelievable that Pat Smullen, Fran Berry and Ruby Walsh have all retired in the space of a month or so, but at least they're all getting out in one piece."
Johnny Murtagh, five-times Irish champion Flat jockey
"Myself and Pat had many a battle over many a year. He was a great jockey, very professional and always a hard man to beat - it was never over until it was over when Pat was involved.
"I'm pleased he's in good health now and as he has said himself, it's on to the next chapter now. It's always sad to see someone retire and I'm sure he had a few more years riding in him, but his health is the most important thing and he has a young family.
"He's a huge asset to the racing world and I'm sure he won't be idle."
Colin Keane, Irish champion Flat jockey in 2017 after titanic tussle with Smullen
"People like Pat and Johnny Murtagh were an inspiration to me growing up and to get the chance to ride against them.
"The battle we had in 2017 was hard work at the time, but I was very lucky to be in that position. Pat is a true gentleman and a great sportsman and I wish him all the best for the future."
Hugo Palmer, trainer of Covert Love, whom Smullen steered to win the Irish Oaks and the Prix de l'Opera in 2015
"I was incredibly lucky to be able to use Pat at a very early stage of my training career really.
"A great mutual friend recommended him and I think his first winner for me was on Short Squeeze in the big Clipper Logistics sprint at York (2014). He delivered him to lead right on the line and it was one of those nerves of steel rides in what was my third season training.
"After that came those great days with Covert Love and Pat also had a great relationship with Gifted Master. It was an honour and a privilege to be able to work with one of the greats of the game."
Pat Smullen's career highlights
Vinnie Roe
Trained by Dermot Weld, Vinnie Roe was a magnificent stayer and gave Smullen his first Classic success when winning the Irish St Leger in 2001. Remarkably they were also triumphant in the following three years. In total Smullen and Vinnie Roe won 13 races together - five of them at Group One level.
Harzand
The Aga Khan-owned colt gave Smullen arguably his biggest success when beating US Army Ranger by a length and a half in the Derby at Epsom in 2016. The Weld-trained three-year-old went on to record a Derby double in the Irish equivalent at the Curragh.
Refuse To Bend
Running in the colours of Moyglare Stud, Refuse To Bend was a landmark first British Classic for Smullen in the 2000 Guineas at Newmarket in 2003.
Rite Of Passage
Yet another high-class Weld stayer, Rite Of Passage was a formidable performer over jumps and on the Flat and enjoyed his biggest day in the hands of Smullen when producing a 20-1 surprise in the Ascot Gold Cup of 2010.
Nightime
Nightime's win in the 2006 running of the Irish 1,000 Guineas was memorable for Smullen and also Weld, as the filly was owned and bred by the trainer's mother, Marguerite. Nightime also won the Coronation Stakes at Royal Ascot.
Free Eagle
Always held in the highest regard by Weld and Smullen, the lightly-raced Free Eagle was give a typically brilliant ride to hit the Group One jackpot in the 2015 Prince of Wales's Stakes at Royal Ascot.