A British man, who Elon Musk called a “pedo” on Twitter, has retained legal counsel and is “preparing a civil complaint for libel” against the Tesla CEO, according to a letter viewed by BuzzFeed News. The letter appears to contradict a claim Musk made on Twitter on Tuesday that he had yet to see any legal repercussions from his allegations, and deepens the problems for the already embattled technology billionaire.

A lawyer for Vernon Unsworth, a UK citizen who was instrumental in the rescue of 12 children trapped in a cave in Thailand, sent Musk a letter earlier this month notifying him of a possible lawsuit, after the Tesla chief’s outburst against his client in July. Musk previously made the allegations against Unsworth without any evidence, before issuing an apology and deleting the offending tweets.

On Tuesday, the Tesla and SpaceX founder reignited the controversy on the social network by suggesting that Unsworth’s lack of legal action against him constituted something suspicious and that his original allegation of pedophilia should be investigated. BuzzFeed News, however, confirmed that Unsworth retained legal representation and sent Musk a letter dated Aug. 6 detailing a possible lawsuit for the “false and defamatory statements.”

“You published through three different tweets to your twenty-two million followers that Mr. Unsworth engages in the sexual exploitation of Thai children, and you did so at a time when he was working to save the lives of twelve Thai children,” writes Unsworth’s lawyer L. Lin Wood, an Atlanta-based defamation expert. “You did so without any basis. According to a subsequent Twitter post, you did so out of anger.”

The possible lawsuit highlights the dangers that Musk could face for his increasingly erratic behavior on Twitter, which has landed him in hot water on multiple occasions in 2018. Earlier this month, Musk unexpectedly tweeted that he was exploring the possibility of taking Tesla private and that he had “funding secured” to do so, igniting a public market frenzy. The bid ultimately went nowhere, and the Securities and Exchange Commission is now reportedly investigating Musk and Tesla over the bizarre sequence of events.

When contacted over email by BuzzFeed News, Musk did not address the legal letter he received.

“Have you actually done any research at all?” he wrote. “For example, you incorrectly state that he is a diver, which shows that you know essentially nothing and have not even bothered to research basic facts.”

BuzzFeed News confirmed with a source familiar with Unsworth that the cave rescuer has diving experience and maintains all the necessary diving equipment.