Al Boum Photo landed the Festival feature in 2019 and 2020, but had to settle for third last year as Minella Indo scuppered his bid to join Golden Miller, Arkle, Best Mate, and Cottage Rake as a three-times winner of the race.
The horse went on to finish second behind Clan Des Obeaux at Punchestown in April and after Mullins opted to sidestep a couple of earlier options this term, the 10-year-old made his reappearance in this Grade Three heat for a fourth year running.
Just four horses started the race - all of them trained by Mullins - with Al Boum Photo sent off the 1/6 favourite in the hands of Paul Townend.
Acapella Bourgeois, who finished second in this race for the last two years, set out to make the gallop with Al Boum Photo sitting on his heels until he jumped into the lead at the eighth fence.
As his stablemate quickly dropped away and was pulled up, Al Boum Photo galloped away in front and while Townend had to shake the reins a couple of fences from home as Burrows Saint tried to move upsides, the winner ultimately had his stablemate well covered.
After clearing the last, Townend just had to keep him up to his work for a four-length verdict.
Mullins said: "He fluffed one fence but did everything else right. Paul said he was just a bit idle in front.
"I'd like to get another run into him but we'll have to see (how he is).
"Burrows Saint ran a cracker and I thought he was going to be a danger, but when Paul pressed the button it was all over.
"Brahma Bull ran well for a horse that would probably hate that ground. Acapella Bourgeois was disappointing so we'll have to see what we do with him."
Coral clipped Al Boum Photo to 12/1 from 14s for the Gold Cup, while he is unchanged at 14/1 with Paddy Power for a third Festival win.
Mullins and Townend were completing a double after the victory of El Fabiolo in the opening David Flynn Construction Maiden Hurdle.
Sent off the 2/7 favourite, El Fabiolo came home 13 lengths clear on what was his debut for Mullins and first run in Ireland having previously been trained in France.
Mullins said: "He's a nice recruit for (owners) Simon Munir and Isaac Souede. He shows me plenty at home and Paul said he was going easy at all stages.
"He does everything easy at home and showed me the same here."
When asked how he would compare with previous maiden hurdle winners for the yard at this track like Laurina and Saint Roi, he added: "He's as good as any of them."