Noble Mission gave Lady Cecil a poignant first Group One success as he continued his own incredible transformation in the Tattersalls Gold Cup at the Curragh.
It is almost a year ago that Lady Cecil took over the running of Warren Place in Newmarket after the death of her celebrated husband Sir Henry, who finished his career by training the equine giant Frankel.
Noble Mission is a full-brother to Frankel and it is only at the age of five he has started to emerge from his sibling's shadow, reaping the benefit of an aggressive ride from James Doyle, also successful in the colours of Khalid Abdullah on Kingman in Saturday's Tattersalls Irish 2000 Guineas.
Noble Mission and Magician went off the even-money joint-favourites and the Aidan O'Brien-trained runner-up closed to a length and a quarter by the post.
The winner had started to earn a slightly dubious reputation in his first three seasons and he was beaten by Cubanita on his reappearance at Newbury.
Front-running tactics worked a treat when he hammered Telescope in the Gordon Richards Stakes at Sandown, and he got the better of the same rival in the Huxley at Chester.
Doyle established a considerable lead turning for home, where Joseph O'Brien started to cajole Magician, and although Noble Mission seemed to be running on fumes inside the final furlong, his initial advantage proved decisive.
As was tradition at Warren Place under Sir Henry Cecil's regime, a flag will now be raised at the yard to celebrate a Group One triumph for the team.
Lady Cecil said: "It's great for all the staff at Warren Place.
"Our big aim was to win a Group One race and to raise the flag for Henry.
"I'm very emotional now. I've almost 30 horses for Prince Khalid and without the horses you just can't do it.
"I'll have to talk to Teddy (Grimthorpe, owner's racing manager) but, to be honest, we didn't think past this about where he might next go.
"He's in the Eclipse at Sandown but we'll have to see how he comes out of this first."
Grimthorpe said: "It's a huge win.
"To win a Group One with Frankel's brother, it's great tribute to those at Warren Place and huge for Juddmonte. It really is a very special day.
"We fell upon the (front-running) plan at Sandown because of needs but it worked again at Chester so we thought must try it again here.
"We need to sit down and have some good thoughts now. He's had four quite tough races, we might need to give him a little bit of a breather but that's up to Jane."
O'Brien said of Magician: "The race was in trouble of losing its Group One status.
"The ground was far from ideal but we had to run as it would be very detrimental to Irish racing to lose a Group One race.
"Joseph looked after him."