Forever Together has shed her maiden tag with a stunning victory in the Oaks at Epsom to give trainer Aidan O'Brien a seventh win in the Classic.

Ridden by O'Brien's son, Donnacha, Forever Together was a 7-1 chance.

O'Brien fielded five of the nine runners on Friday (Saturday AEST) and it was Bye Bye Baby who cut out the early running.

She began to falter early in the home straight and was swiftly passed by Forever Together and the 5-2 favourite Wild Illusion.

It was soon clear Forever Together had far more to give and she came home 4-1/2 lengths clear of the market leader.

It was a second Group One success for Donnacha O'Brien who won the 2000 Guineas for his father aboard Saxon Warrior.

"Forever Together was very impressive," he said.

"It played out perfectly. She is very genuine and galloped out to the line really well. She is a proper staying filly.

"When you are riding one of his (father's), you have a chance. It does not matter what it is. He is an absolute genius and is able to do things with these horses that I don't understand.

"He just tweaks little things and brings out massive improvement. I don't know how he does it, but I am trying to learn as much as I can."

Aidan O'Brien said the winner was a true stayer.

"She caught the eye at Chester, She's a staying filly and got the trip very well," he said.

"I was very happy with all the fillies really.

"It's incredible what Donnacha is doing and we're grateful to a lot of people who work hard every day.

"Donnacha has always been a very good rider.

"He's been watching racing since he opened his eyes so tactically he's very aware. He can make his own decisions and stand by them."