The Avengers star has returned to the Great White Way in the Arthur Miller revival, opposite Danny DeVito, Jessica Hecht, and Tony Shalhoub.

Obama and his eldest daughter Malia decided to check out the production while in New York City in late February (17), shortly after The Price began previews, and the surprise visit caught Ruffalo off-guard.

"It was pretty amazing," he recalled of meeting the former leader. "I didn't know he was gonna be there. I'm on the fifth floor (of the theatre) in my dressing room, so I come running down..., barrelling down the stairwell, yelling, and there were four Secret Service guys standing there, like (staring at me).

"So I walked into Danny's dressing room, like, 'What's up with the Secret Service?' I was like, '(Is it Vice President Mike) Pence?' (Danny said), 'No'. '(President Donald) Trump?' 'No'. 'Who?' 'Obama, you idiot!'"

Although Ruffalo, an outspoken Democrat, was excited about performing for Obama, the unexpected appearance was also a distraction while the star was onstage.

"It's hard not to wanna look at him," Mark smiled on U.S. breakfast show Good Morning America. "He's the show, but he was beautiful, they came backstage and were really kind to the cast and crew. He's a big fan of Arthur Miller's."

"It was a really sweet moment. Bittersweet," he added.

The Price marks Ruffalo's first Broadway gig in a decade, following his role in a 2006 revival of Clifford Odets' Awake and Sing!, and he reveals the show came at just the right time as his next superhero outing as Bruce Banner/The Hulk was postponed.

He explained, "I was looking to do a play. Avengers (Avengers: Infinity War) pushed (got delayed) for a couple months, and someone said to me, 'What would be your dream right now?' I said, 'I wanna get back on the stage with a great group of actors, just a straight play, no bells or whistles, just actors going at it on a stage'. And the next day I got an offer for this play. An actor fell out of it (sic) and they needed someone really quickly... and my prayer was answered."

Ruffalo replaced fellow movie star John Turturro in early January (17), after The Night Of actor had to withdraw from the Roundabout Theatre Company production due to a scheduling conflict.

The Price officially opens next week (16Mar17) at the American Airlines Theatre.