In an explosive Substack post titled “The Trouble With Elon Musk,” Harris detailed his fallout with his former friend, publishing texts exchanged during the coronavirus pandemic’s early days.

He cites one incident where the Tesla CEO bet him $1 million against a $1,000 bottle of tequila that the U.S. wouldn’t see as many as 35,000 cases of COVID-19.

Harris said he tried to up the bet to 3.5 million cases of COVID-19 at the time, but Musk accused him of “having lost [his] mind” and insisted on sticking with 35,000 cases.

After the CDC reported 35,000 deaths from COVID-19 a few weeks later, Harris said he texted Musk: “Is (35,000 deaths + 600,000 cases) > 35,000 cases?”

The text went unanswered, according to Harris, who cites the message as the end of their years-long friendship.

“Let this be a cautionary tale for any of Elon’s friends who might be tempted to tell the great man something he doesn’t want to hear,” Harris said in the post.

Musk publicly criticized the early concerns surrounding COVID-19 in 2020, stating in an X post, “The coronavirus panic is dumb.”

As the pandemic spread, he became increasingly skeptical of COVID-19 vaccines and also attacked former chief medical advisor to the President of the United States, Anthony Fauci, who oversaw the country’s response to the pandemic.

In December 2022, Musk called for Fauci’s prosecution, posting on X: “My pronouns are Prosecute/Fauci.”

Representatives for Musk did not immediately respond to a request for comment from Fortune.

Harris and Musk: Friends to Foes

Harris and Musk were friends for years before the alleged fallout.

In his Substack post, Harris said he knew Musk in 2008 when Tesla was struggling to make payroll, and Musk was “living off loans from his friends Larry [Page] and Sergey [Brin].”

He praised Musk as a remarkable person who was “probably the most likely to remain a world-historical figure” but also “the most likely to squander his ample opportunities to live a happy life, ruin his reputation and most important relationships, and produce lasting harm across the globe.”

Over the past few years, the two have traded public barbs.

Musk has attacked Harris on X, calling him “mentally ill” and “an utter idiot.” Harris has called the billionaire a bully and alleged his former pal is addicted to social media.

In an episode of “The Bulwark” podcast released in November last year, Harris said the billionaire was “snorting ketamine and tweeting at all hours of the day and night.”

Harris criticized Musk’s social media use again in the recent post.

“Any dispassionate observer of Elon’s behavior on Twitter/X can see that there is something seriously wrong with his moral compass, if not his perception of reality,” he said.