Aidan O'Brien has admitted he was "shell-shocked" at the decision to retire Holy Roman Emperor to stud at Coolmore to replace George Washington following the discovery that last year's 2000 Guineas hero has fertility problems.

The Danehill colt had been second-favourite for this year's Newmarket Classic behind his old adversary Teofilo.

Holy Roman Emperor clashed twice with Jim Bolger's Teofilo in his two-year-old season, the latest in a titanic battle for the Dewhurst at Newmarket in October.

His four wins included the Phoenix Stakes at the Curragh and the Grand Criterium at Longchamp.

O'Brien told PA Sport: "The lads and the boss (John Magnier) had to try and replace him. We were shell-shocked about it here because Holy Roman Emperor was our best horse.

"He was the horse we were looking forward to for the Guineas and the St James's Palace.

"Paul Shanahan was here at 11.30am and the box came and picked him up at 11.50am. I spoke to the boss in between and the more I tried to persuade him not to retire him, the more he was convinced he had to retire him.

"The boss has his clients there and has to take care of them and obviously they are trying to replace like with like. It's a big shock to everyone here. We are a racing stable and everyone here does their best every day to make it happen.

"We have been very happy with him and we were looking forward to the Guineas. What can I say? It was really out of our hands and there was nothing we could do about it.

"It's a bit like having a team getting ready for the premiership and your striker's soul being taken away. He was by far our best horse, the others have to make the jump still. He handled all types of ground, he ran in the Dewhurst on soft when we were nearly not going to run him. He got into traffic trouble on soft ground and still only just got beat and looked very unlucky.

"Obviously we were looking forward to going back for the Guineas and we thought he was ready made for the St James's Palace after that. That was made for him.

"It's a sickener, but it's a business decision. The lads have been in business a long time and have a lot of very important clients. He is a Danehill with a super physique, he has everything. With all the mares booked to George they felt they had to pull out all the stops for the people.

"He had speed, he had everything. He was well forward, we were going along lovely. Hopefully, some of the others will improve - we'll keep trying."

A statement from Coolmore said: "In the very early stages of George Washington's stud career, his fertility has been questioned. Coolmore brought in veterinary expert Dr Dixon Varner from the USA to consult on the matter and are awaiting prognosis.

"George Washington has been suspended from covering and Holy Roman Emperor, another dual Group One-winning two-year-old by Danehill and Ballydoyle's leading 2000 Guineas prospect, has been retired to take his place."

Coolmore's Christy Grassick said: "We are fortunate to have a horse of Holy Roman Emperor's calibre to take over in order to facilitate our clients with mares booked to George Washington."

Neil Morrice, on-course representative for Stan James, sponsors of the Guineas, said: "The news from Ballydoyle about Holy Roman Emperor is a blow to the hordes who were looking forward to watching him lock horns with Teofilo again as a three-year-old.

"His defection has given the race a red-hot market leader in Teofilo, who is unlikely to meet Dutch Art until Guineas day."

Stan James 2000 Guineas, sponsors bet: 6-4 Teofilo, 7-1 Dutch Art, 12-1 Mount Nelson, 14-1 Strategic Prince, 16-1 Authorized, Eagle Mountain, 20-1 bar.

William Hill: 11-8 Teofilo, 8-1 Dutch Art, 12-1 Strategic Prince, Mount Nelson, 16-1 Authorized, Eagle Mountain, Adagio, 20-1 Duke Of Marmalade, Haatef, 25-1 Truly Royal, 33-1 bar.