Noble Mission showed tremendous tenacity as he emulated big brother Frankel by winning the Qipco Champion Stakes at Ascot.
The son of Galileo and Kind has thrived over his optimum trip of ten furlongs this season and also had the opportunity to race on his favoured testing going at the Berkshire track.
The five-year-old, trained by Jane Cecil, will always live in the shadow of Frankel but he enjoyed his finest hour as he made all of the running in this Group One showpiece.
Noble Mission (7-1) pulled out all the stops for James Doyle to hold off Al Kazeem (16-1) by a neck after an epic duel.
Free Eagle (5-2) stayed on strongly for third place, a length and a quarter behind.
Frankel ended his racing days with victory in this race two years ago, when trained by the late Henry Cecil.
For the final couple of furlongs it appeared as if the revitalised Al Kazeem was about to wreck what was later described as a "fairytale" as the pair fought tooth-and-nail.
But Doyle found that vital neck more than Al Kazeem and George Baker, who high-fived his colleague as soon as they had crossed the line in virtual unison.
Noble Mission (7-1) had already allowed Cecil her wish of raising the ancestral flag her husband always flew after Group One winners when he claimed the Tattersalls Gold Cup in Ireland, but it was obvious to anyone this was a moment of far greater importance.
Doyle adopted the same approach which has seen the five-year-old make such progress this season, sending him to the front immediately.
And with Al Kazeem always on his tail, that pair were the only two to really feature.
They were, though, an ample cast for a memorable spectacle.
"I was interviewed before the race, which I didn't really want to do, and I said it would be a fairytale," said Cecil.
"That's what it feels like to me.
"We hardly dared to dream. We knew he was in great shape but it was a tough race.
"What makes it so much more special, being Frankel's brother.
"A year ago, who would have though Noble would have been here today winning the Champion Stakes.
"It was nerve-racking, that last little bit.
"James rode a brilliant race. I had my head in my hands because I didn't think he would hang on, but he was so brave."
Noble Mission was given a warm and enthusiastic welcome back to the winner's enclosure, and she said: "I know a lot of that was for Henry, it's so wonderful. You can still feel all the love that everyone has for Henry."
Teddy Grimthorpe, racing manager for Khalid Abdullah, a loyal supporter of the Cecil family, said: "What a happy day - it's the emotions of the whole thing - with Jane, and the history of Champions Day with Henry, and the brother of Frankel.
"It's just an unbelievable story.
"He's matured mentally and physically. I wanted to actually run in a race in America, but the Prince said, 'No, save him for Champions Day'.
Plans remain fluid, as Grimthorpe added: "I don't know what he'll do now. I'd have said that was it for the year, but he could race on.
"It's in the Prince's hands."
One blot for Doyle was the receipt of a seven-day ban (November 1, 3-8) and a £10,000 fine for over-use of the whip.
Roger Charlton could not have been prouder of Al Kazeem, who returned to training after proving subfertile at stud and was beaten under six lengths in the Prix de l'Arc de Triomphe.
He said: "What can you say? He didn't get the credit for the Arc run, and he's run as well as he ever has today.
"I thought after the Arc he'd be a Cup horse for next year, but he can go a mile and a quarter or a mile and a half.
"He'll have entries for Hong Kong and Dubai, and we'll see. It shows they can come back."
Lightly-raced Free Eagle stuck on well for third and trainer Dermot Weld said: "He just wasn't at his best on that ground, but his sheer ability kept him there - he has been beaten a length and a quarter.
"It was a fantastic horse race. There's a lot to look forward to and I'd imagine I'd start him off in the Tattersalls Gold Cup at the Curragh."
Cirrus Des Aigles (7-4 favourite), a former winner back for a fourth tilt, was only fifth.
Jockey Christophe Soumillon said: "He had a good run but unfortunately I didn't have any power when I came into the straight.
"It was a run for nothing, it just happens sometimes with horses. The ground was not to blame."