Paul Bettany had to be careful about what he ate while shooting 'WandaVision' because of his tight-fitting costume

Speaking to Stephen Colbert on 'The Late Show', he said: "But the interesting thing is what you discover, is that you can't join in the sort of COVID pandemic banana bread-eating phantasmagoria.

"Because when you wear the muscle suit, and you have a banana bread belly, it's very obvious. The jig's up."

The 56-year-old host seemed surprised that producers couldn't digitally alter his appearance.

He asked: "They can't just digitally take that out with your ears?"

His guest laughingly replied: "Maybe they can! I mean, for god's sake, Mark Ruffalo—you couldn't pull him away from the craft service table."

Stephen was also keen to know how much of the impressive chest Paul displays in the show is his own and how much his muscles had been enhanced, and the actor admitted he had had some help.

Paul replied: "I'm going to get very specific with you now.

"About 42 inches of it is my chest. About eight inches just isn't. But it's not digital. It's a suit that, you know, you wear. They they give you a muscle suit. It's not mine.

The host exclaimed: "You've just made me the happiest man and I can't wait to tell my wife."

Meanwhile, Paul has admitted he "absolutely" didn't expect 'WandaVision' to be such a huge hit.

He told Ellen DeGeneres: “We thought that we were going to be sort of the kooky cousin in the Marvel universe, and it’s been really extraordinary."

He also paid tribute to the fans of the Disney+ show, who he credited for making it "this phenomenon".

He added: "I am so thankful for that. It's been an incredible ride.”