The Aussie actor started guzzling water before performances, to fight dehydration headaches, but it left him desperate for a pee during the show.
And one night, he just couldn't hold it in.
He tells Playboy magazine, "I thought, 'I'll be all right.' The number featured (character) Belle and me; I chased her around the stage, lifting her up, dragging her, singing the whole time. Then I realised, 'No way!'
"I was sucking in air, trying to sing and dance. I picked her up and realised I peed my pants a little. The very last note is a big time F sharp... (and) you have to release certain muscles to hit it, the same ones that allow you to hold on when you have to go to the bathroom.
"I thought, 'S**t, if I sing this note, I'm going to pee my pants; if I don't, I'm going to look humiliated. The actor in me took over."
Jackman thought he'd got away with it when he looked down and saw no trace he'd relieved himself onstage: "I thought, 'These red tights must be waterproof'. I was laughing as if I'd gotten away with it. But the audience was looking at me funny. It had seeped through and my pants were completely wet."