Elon Musk revealed through text on Friday that he declined to work on climate change with Bill Gates because the Microsoft co-founder was shorting Tesla.

The two billionaires appear to be planning a meeting before Musk asks Gates if he still has a “half-billion-dollar short bet against Tesla” in the texts.

Gates replies, “Sorry to say I haven’t closed it yet,” adding in another text: “I would like to discuss philanthropy possibilities.”

Musk responds that he can’t take Gates’ climate change philanthropy seriously because he “has a big short position against Tesla, the company doing the most to tackle climate change.”

Musk confirmed the accuracy of a screenshot of the text exchange provided by @WholeMarsBlog on Friday night, who wrote “No idea if this is legit lol” and inquired about it.

“Yeah,” Musk answered, “but I didn’t leak it to NYT. They must have got it through friends of friends. I heard from multiple people at TED that Gates still had half-billion short against Tesla, which is why I asked him, so it’s not exactly top secret.”

Shorting is when an investor borrows stock with the expectation that it will fall in value, resulting in a profit.

Musk also attacked Gates on Friday, equating a photo of the Seattleite to a pregnant man emoji in a filthy tweet.