The 27-year-old promised fans he'd take off all his clothes and jump into the Zambezi River if he reached his target amount during the Hell and High Water BT Red Nose Challenge.
The star kept to his word and bashfully waded through the water while preserving his modesty with his hand.
BBC Radio 1 also shared a picture of a naked James on its Twitter and wrote: "The only thing to say about this tweet @gregjames is naked getting into a river!"
James completed the five-day trek along with Dara O'Briain, Melanie C, Jack Dee, Chelsee Healey and Phillips Idowu. The celebrities travelled 111km down the Zambezi River and battled rapids during the challenge.
Speaking about the ordeal, James said: "The rapids are really frightening, especially if you're a novice! You can't just sit back, you have to keep paddling otherwise you'll just float off and go miles away.
"We're in a big raft today and it keeps bouncing around, people are popping out of it like popcorn! I bounced into the air earlier and was only saved by Phillips grabbing me with his massive athletic claw!
"But we're here, we've been doing this challenge and we all look like idiots, but the point is to raise a lot of money for the people we've been meeting out here. And I know it sounds really cheesy, but I totally get it - I get Comic Relief properly now. I've always watched it on telly, but I've seen it now first-hand. It's really touching, really lovely."
Taking to Twitter, he added yesterday (February 3): "Tired, bruised, burnt, bitten, battered and still a bit smelly but so proud of our whole team. HOME. We did it. Happy boy"
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