MrBeast had teamed up with the Arbor Day Foundation to try and plant 20 million trees, setting himself a target of $20m in donations to achieve that goal.
"We hit like $6m in the first few days, and it started to slow down," MrBeast told the channel before adding that Musk came out of the blue to reply to one of his tweets.
"And he's just like, 'oh, this looks interesting,'" he said.
MrBeast then shared that his friend and fellow YouTuber Marques Brownlee told the tech billionaire more about the project.
"Marques was like, 'This is cool, you should donate,' and he was like, 'Sure, why not?'" MrBeast continued.
"And then Elon just donated a million dollars."
Due to Musk's interest in the project, it also meant that donations from other people also came flooding in.
Musk wasn't the only person to offer the YouTuber big bucks.
MrBeast recently told the FLAGRANT podcast that someone offered him $1bn for his channel.
Speaking to the host Andrew Schulz, he shared that there's been a few people interested in purchasing his channel, but he wasn't interested in the offer.
"Like you know, 'a billion dollars if we could own the channel and the companies' and stuff like that. And I'm like, 'oh, that sounds enticing, but I don't know if I want to work for my YouTube channel.'"
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