A British cave diver who helped rescue 12 boys and their coach in northern Thailand says he’s considering legal action against billionaire entrepreneur Elon Musk who called him a pedophile online.

Vern Unsworth, a British cave explorer based in Thailand, helped rescuers navigate the complex Tham Luang cave system where the boys and their coach were trapped for more than two weeks beginning in June.

On Sunday, Musk unleashed on Unsworth, writing on Twitter that he intended to build the child-size submarine he offered to rescuers for the Thailand mission that they rejected.

“We will make one of the mini-sub/pod going all the way to Cave 5 no problemo [sic],” he wrote in a tweet that has since been deleted. “Sorry pedo guy, you really did ask for it.”

The founder and CEO of tech giants Tesla and SpaceX didn’t provide any further explanation or context for the accusation. It’s unclear what provoked the outburst, but earlier this month Unsworth spoke critically of Musk’s miniature submarine design in an interview with CNN.

“It just had absolutely no chance of working. He had no conception of what the cave passage was like,” he said. “The submarine, I believe, was about five-foot-six long, rigid, so it wouldn't have gone round corners or round any obstacles.”

Unsworth went on to say that Musk’s offer to help the mission was simply a “PR stunt” and that he could “stick his submarine where it hurts.”

Musk’s “pedo” tweet attracted immediate backlash with many users calling him out for hurling serious and unfounded accusations for all of his 22 million followers to see.

In response to one tweet, the American businessman wrote: “Bet ya a signed dollar it’s true.”

No evidence has come to light to substantiate Musk’s pedophilia accusation.

In an interview with Australian broadcaster Nine Network, Unsworth said he was considering legal action against Musk for the comment.