The John Gosden-trained African Dream was pulled up with a pelvic injury in the finale to Gold Cup day, it has been confirmed.
The 9/4 favourite for the Sandringham Stakes appeared to lose her action a over a furlong from home and was eased down by jockey Kieran O'Neill.
Reports from the track suggested she walked into the horse ambulance and was taken to the racecourse stables.
A spokesperson for Ascot said this evening: "African Dream sustained a pelvic injury in the concluding Sandringham Handicap.
"She has been taken to the stables and is in a stable condition."
From the yard that won the feature Gold Cup for the third year running with Stradivarius, the daughter of Oasis Dream was one of the shortest-priced contenders on the seven race card.
She had more than a stone in hand of her rivals on the form book before the handicap debut, following a bold run a week ago.
Victory in the mile event went to Hayley Turner and Charlie Fellows for the second year in a row, with 33/1 shot Onassis.
Turner is one of only two female jockeys to have ridden a winner at Royal Ascot and her mount, a daughter of 1,000 Guineas runner-up Jacqueline Quest, scored by a length and a quarter.
"Onassis felt really good," Turner said.
"She had the perfect profile for the race - the same as Thanks Be last year - and Charlie (Fellowes) told me she would win it about three months ago!
"She took the conditions really well and took her time.
"She is a very nice filly and did it easily."
Stradivarius is now the third horse to win the highlight of the royal meeting on three occasions, joining Sagaro and Yeats.
He effortlessly cruised clear of his rivals under Frankie Dettori to come home ten lengths clear.
