Bradley Cooper confesses to going commando at White House state dinner

Bradley Cooper is admitting to a bit of a White House wardrobe mishap.

The actor was among the attendees at last week’s state dinner in Washington, but confessed on "The Ellen DeGeneres" show Monday that he had some trouble getting into his tux before the event.

"I'm prepping for this new movie and I'm trying to gain weight fast, so I've gained about 15 pounds in four weeks and nothing fits me anymore," the "American Hustle" star, 39, explained. "So I wore the tuxedo I wore to the Golden Globes. I just sort of threw it in the bag and brought it and went to Washington D.C. and then I'm getting dressed like 10 minutes before I was supposed go, and literally the pants go up to like here [gesturing to his upper thighs]. And I just started laughing, like, 'This is hilarious, I'm going to meet the president.'"

So the Oscar nominee went to the White House without underpants.

"I had to go commando...because there was no room at all. I did. I had to," Cooper said. "And you're sitting there and it's a lot of getting up [to greet people]. You know what I mean? And I couldn't stand up really."

"It was a nightmare. But I made it through," he added.

Cooper -- apparently sans boxers or briefs -- attended the White House state dinner, hosted by President Barack Obama and first lady Michelle Obama in honor of French president Francois Hollande, with girlfriend Suki Waterhouse. Other celebrities on the gala's guest list included Mindy Kaling, Julia Louis-Dreyfus and Stephen Colbert.

Watch Cooper's "Ellen" appearance below: