During a Tuesday appearance on The Late Late Show, the 49-year-old actor detailed to host James Corden how it all went down on the post-rehearsal-dinner party bus the night before his "I do"s with Audra Mari in North Dakota.
"So I think I'm gonna hang from the rafters inside this party bus and start crowd surfing across the top of it, and I throw my back out," recalled Duhamel, adding that he couldn't "get up out of bed" the next morning — a.k.a. the day of the wedding.
"The one day you have to be able to walk is down that aisle," said the Shotgun Wedding star. "And it was, like, touch and go right up until an hour before the wedding."
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The Late Late Show with James Corden/YouTube Josh Duhamel
Duhamel went on to say he got "shot up" with medication at the emergency room — which got him through the wedding, as he was "fine the whole night."
"And then woke up the next morning, couldn't get out of bed again," he said.
Joked fellow guest Judy Greer, "For other reasons ... ", leading to laughter from Duhamel, the audience and Corden, 44.
As for how his back is doing now, Duhamel said, "It's pretty good."
"It's on!! She found a message in a bottle that washed ashore and said YES!! @audramari," the actor captioned the shot of the pair smiling, while he held up a handwritten letter that read, "Audra Diane Mari Will You Marry Me?"
Representatives for Duhamel did not immediately respond to PEOPLE's request for comment, but a source who went told PEOPLE the pair had "a great time" and that the evening "was lovely."