Mark Ruffalo on former President Obama surprising the cast of 'The Price' on Broadway

"I didn't know he was going to be there," Ruffalo said on "GMA."

— -- Fans know him as the Hulk and now Mark Ruffalo is starring in a Broadway show alongside Danny DeVito.

"'Avengers' pushed for a couple months and someone said to me, 'What would be your dream right now?' and I said, 'I want to get back on a stage with a great group of actors,'" Ruffalo said today on "Good Morning America." "Just a straight play. No bells and whistles, just actors going at it on a stage. And the next day, I got an offer for this play."

In "The Price," a play by Arthur Miller, Ruffalo stars as "Victor Franz," a character who gave up his dream to support his father during the Great Depression. The cast includes Tony Shalhoub ("Walter Franz"), Jessica Hecht ("Esther Franz") and Danny DeVito ("Gregory Solomon").

"Arthur Miller generally isn't thought of as comedic, but this is probably one of his most comedic plays," Ruffalo said of the playwright. "There's a whole act between Danny [DeVito] and I that brings the house down every night and he is incredible in this. He is amazing...this is Danny's Broadway debut."

The cast gave preview performances of "The Price" in February. One night, special guest and former president Barack Obama and daughter Malia attended the show.

"It was pretty amazing, I didn't know he was going to be there," Ruffalo said. "[I] came running, barreling down the stairwell yelling and there were four Secret Service guys standing there. I walked into Danny's dressing room like, 'What's up with the secret Service?' I was like 'Pence?' He's like, 'No.' 'Trump?' No. 'Who?' 'Obama, you idiot!'"

"But he was beautiful," Ruffalo added. "They came backstage and were really kind to the cast and crew. He's a big fan of Arthur Miller's and yeah, it was a really sweet moment."

"The Price" opens on Broadway March 16.