Investec Oaks winner Taghrooda will run in the King George VI And Queen Elizabeth Stakes at Ascot on 26 July rather than go for a Classic double in the Darley Irish Oaks at the Curragh on Saturday.
The John Gosden-trained filly beat Dermot Weld's Tarfasha in the Epsom showpiece, with both fillies owned by Sheikh Hamdan Al Maktoum.
Taghrooda was odds-on favourite for the Curragh but instead tackles older horses and colts in Britain’s mid-summer showpiece.
Sheikh Hamdan's racing manager Angus Gold said: "Sheikh Hamdan has now decided that he would like to run Taghrooda in the King George at Ascot and therefore she will not be declared for the Irish Oaks.
"Tarfasha will be declared for the Irish Oaks.
"Taghrooda will be retired to stud at the end of this year and Sheikh Hamdan thought he would like to take his chance in the big one, she's in good form and she gets plenty of weight from the older horses.
"It was tempting to go to Ireland and try to win another Oaks, but we have a filly there and it's possibly not the strongest King George ever and Sheikh Hamdan was keen to give her a chance there."
Heading the betting for the King George is Michael Stoute's Telescope after his impressive win at Royal Ascot, and Harry Herbert, racing manager for owners Highclere Thoroughbred Racing, admits the decision to run Taghrooda makes his task harder.
"It's exciting and adds more spice to the race, I don't think any of us saw it coming," he told At The Races.
"I thought she was a shoo-in for the Irish Oaks and having a horse like Telescope in the King George, your first reaction is 'ouch'.
"I'm delighted it will make the race spicier, but a little concerned as she's a really good filly.
"It would probably only happen in this country that a three-year-old filly takes on the older colts.
"I thought it was an awesome performance in the Oaks, she's a magnificent-looking filly and I'm sure this has been carefully thought out."