Hot Snap came from last to first as she gave trainer Sir Henry Cecil a big boost with victory in the Nell Gwyn Stakes at Newmarket.
The 10-1 chance, ridden by Tom Queally, ran a noteworthy 1000 Guineas trial.
She triumphed by two and a quarter lengths from favourite Sky Lantern.
Cecil, who guided the unbeaten Frankel to 14 career wins before the colt's retirement in October, has been fighting stomach cancer for several years.
But Hot Snap, now 5-1 joint favourite with Just The Judge from 33s for the Guineas on 5 May, could give him the chance of a 26th British Classic victory.
Queally was still in last place with two furlongs to go, but tracked Sky Lantern and surged past the 11-4 favourite, with Winning Express (11-1) third.
Hot Snap, owned like Frankel by Saudi prince Khalid Abdulla, had won her only previous race, a one-mile maiden fillies' stakes over a mile at Kempton in September.
But she looks to be on the upgrade for Cecil, who has won the 1000 Guineas six times, with the last triumph coming in 1999 with Wince.
Hot Snap is a half-sister to star mare Midday, formerly trained by Cecil, who was confirmed as being in foal to Frankel on Tuesday.
Earlier at Newmarket, the Richard Fahey-trained Garswood (5-2 favourite) landed the European Free Handicap under Tony Hamilton.
On a day of Classic Clues, Andre Fabre sent out a rare Newmarket runner in Intello and duly won the Feilden Stakes with the 6-4 favourite, who will be given an entry in the French Derby.
Meanwhile, over the jumps at Cheltenham, 15-8 favourite Champion Court beat Menorah by three-quarters of a length in a thrilling finish to the Silver Trophy.