Wesley Ward believes that Acapulco will enjoy "the best of both worlds" by being trained by Aidan O'Brien as well as mating with Galileo.
Winner of the Queen Mary Stakes at Royal Ascot in 2015, her three-year-old season was interrupted by injury and she missed the chance to run in England last summer.
But as she already had a date with Galileo lined up, Ward suggested the switch to O'Brien would be best for all parties, with a tilt at the King's Stand at Royal Ascot the chief goal.
"I really thought she'd win at Royal Ascot again last year as everything had gone so smoothly with her," said the American handler (pictured).
"She won her prep race and then stepped up to win a stakes race really easy and I was so confident.
"Then, when we get her over there she had an abscess on her foot and we spent the rest of the year trying to build it back up.
"With everyone from Coolmore being at the Breeders' Cup we tried to get her ready for a race that weekend but it was a bit of a rush. She ran well but was just a few breezes short.
"She was perfectly sound afterwards, though, and that's what pleased us so much. I said afterwards there was still plenty she could achieve.
"Obviously, when you have a date with Galileo you don't want to miss it but we all talked and by having Aidan train her she gets the both of both worlds as there's no better trainer.
"It would be a lot to ask of her to go and see Galileo and then come back and race for me so it's best she stays in Ireland.
"Coolmore have been brilliant to me, they really have, and while I'm sad to lose her, it's for the best.
"I had a chat with Aidan about her at the Breeders' Cup and I'm looking forward to seeing what she can do."
Meanwhile, Brian Hughes followed up his treble at Ayr on Monday with another three-timer at Musselburgh yesterday.
Hughes, who secured a five-timer at the East Lothian track in November, won both divisions of the Racing UK-sponsored maiden hurdle, on Idder (9/2) and Fattsota (4/6 favourite), and the closing bumper on Kevin Ryan's impressive Beyond The Clouds.
Idder may have been fortunate as the front-running Stipulate, which finished second, nearly came down at the third-last.
"I think I might have won anyway as I was going very well when the other horse made a mistake," said Hughes.
"To be fair, he was idling all the way up the straight. He was a decent horse on the Flat. Jimmy Moffatt's picked him up and he'll be a good, fun horse."
Beyond The Clouds (4/1) was by far the most impressive of the three horses, winning by 12 lengths on debut.
Brian Harding struck with the Keith Dalgleish-trained Dream Flyer (11/4) in the Alex Donaldson Memorial Handicap Chase, but missed a nice winner when stablemate Mixboy (6/4 favourite) jumped his rivals into submission in the Kilmany Cup Handicap Chase.
Harding took a fall in the previous race from Shotofwine, which, like Mixboy, is owned by Paul and Clare Rooney.