Fastorslow, trained by Martin Brassil, has twice got the better of Galopin Des Champs but the reigning champion came out on top last time in the Irish Gold Cup.
“Galopin des Champs came out of his last race very well and I am very happy,” said Mullins, who also won the race with Al Boum Photo in 2019 and 2020.
“It’s going to be a tip-top Gold Cup and we are in great form.”
Willie’s son Patrick, who rode the trainer’s historic 100th Festival winner on Wednesday, will be aboard stablemate Monkfish.
A fascinating race sees a host of contenders and plenty of question marks.
Gentlemansgame has not run since defeating Bravemansgame in the Charlie Hall Chase more than four months ago, but the grey cannot be discounted in the hands of shrewd trainer Mouse Morris.
The Real Whacker clocked up a third course victory when edging out Gerri Colombe to win the Brown Advisory Novices’ Chase at last year’s Festival. They both return along with the 2022 novice chase winner L’Homme Presse.
Grand National winner Corach Rambler, Welsh National victor Nassalam and Rachael Blackmore’s mount Jungle Boogie also line up.