Frankie Dettori will ride Gold Cup winner and former Melbourne Cup favourite Order Of St George in the Prix de l'Arc de Triomphe at Chantilly.

Dettori, who is chasing a fifth win in Sunday's European showpiece, had been provisionally booked by trainer Dermot Weld for the 2015 Champion Stakes winner Fascinating Rock who was ruled out earlier in the week.

"I've picked up the ride on Order Of St George and I'm every bit as thrilled as I was when I rode Camelot (for O'Brien) in the race four years ago," Dettori said in his blog for Ladbrokes.

"I was getting a bit anxious that I might miss out on an Arc ride after Fascinating Rock failed to make the race so I am delighted that Aidan has asked me to ride for him again.

"Postponed is clearly the biggest threat. It's difficult to see any flaws in the favourite but my horse is trained by a genius. "

Part-owned by Australian Lloyd WIlliams, Order Of Ste George had been favourite for the Melbourne Cup untll he received top weight and was set for the Arc instead.

O'Brien is also set to saddle Found and Highland Reel, who are expected to be ridden by Ryan Moore and Seamie Heffernan respectively in a race that will see a maximum of 16 runners.

Postponed is unbeaten in four starts since joining Roger Varian, enjoying Group One victories in the Dubai Sheema Classic, the Coronation Cup and the Juddmonte International.