Estimate returns to the scene of her greatest triumph when going on a retrieval mission in the Qipco British Champions Long Distance Cup at Ascot on Saturday.
The Queen's admirable stayer lifted the Gold Cup at Royal Ascot in 2013 and was second this summer only to be disqualified after testing positive for a banned substance caused by contaminated feed.
She goes back to the Berkshire course on the back of victory in the Doncaster Cup and now tries to erase the memory of her under-par run in this race last year.
"I'm very happy with Estimate. She loves Ascot, but she will have to take on Aidan's (O'Brien) Gold Cup winner, Leading Light, and he is a very good stayer, no doubt about that. He'll be hard to beat, but we think we're in very good shape," said trainer Sir Michael Stoute.
"Estimate disappointed last year in soft ground but we found she had an injury. Monsun's (progeny) usually like soft ground so we'll give it a shot. It just wasn't conclusive last time."
Estimate also won the Queen's Vase over this course and distance in 2012, a race Leading Light won last year on his way to taking the Ladbrokes St Leger.
Leading Light landed the Gold Cup this year but O'Brien's charge was only runner-up to Brown Panther in the Irish St Leger on his latest start.
There is a second Irish challenger in Dermot Weld's Forgotten Rules, who is unexposed, having won a bumper at Punchestown in April and a Flat race at Galway in the summer on his only two outings.
"He's a totally unexposed horse, but we've always thought he was very good," said his jockey Pat Smullen.
"His lack of experience might count against him in a race like this, but we hope he can develop into a high-class stayer and one thing we do know about this horse is he won't mind the ground. I'm hoping he'll go there and run a big race."
Big Orange has made giant strides since finishing fourth to Hartnell in this season's Queen's Vase. Michael Bell's runner has won at Chester and at Ascot and the trainer believes the three-year-old is still progressing.
"He has been is good order since his Ascot win. He has got two very good bits of form at Ascot and is improving all the time," said the Newmarket handler.
"I thought that his latest win was a very good performance as he was giving 3lb to the other two horses involved in the photo finish, which is effectively four lengths over that distance. It certainly warranted supplementing him for this race.
"He has an extra quarter-mile to travel on Saturday, but he ran very well over this trip in the Queen's Vase so the longer trip should not be detrimental to him.
"When he won at Chester the ground was on the slow side. I have always thought he will be more comfortable on this kind of ground rather than the other extreme. And anyway, he will get the best of the ground as it is the first race and Ascot have kept a fresh strip of ground for this meeting.
"I have never had a winner on Qipco British Champions Day before and to do so would be huge. It would bring enormous pleasure to everyone involved."
Biographer was not disgraced in this race last year when sixth to Royal Diamond and his trainer David Lanigan can see him acquitting himself creditably.
"He's been going fine and has had a nice prep, so hopefully he will give a good account of himself," said Lanigan. "He was only beaten about two lengths in this race last year. He won his Listed race on soft ground there."
