Elon Musk just lobbed another grenade in his ongoing feud with Bill Gates, and this time it wasn't even about anything Gates did to Tesla directly.

When the Gates Foundation disclosed a massive reduction in its Microsoft (MSFT) holdings—dumping 65% of the position for $8.8 billion—the Tesla CEO saw an opening to revive one of tech's most personal grudges.

From Microsoft Sales to Tesla Shots

On November 15, stock tracking account Barchart posted on X about the foundation's eye-popping Microsoft sale. According to the Q3 13F filing with the Securities and Exchange Commission, the Gates Foundation slashed its position by 17,073,499 shares, a 64.91% reduction.

Tesla Owners Silicon Valley reposted the news with a cheeky observation: "Dang, Bill is covering his $TSLA short."

That was all the invitation Musk needed.

"If Gates hasn't fully closed out the crazy short position he has held against Tesla for ~8 years, he had better do so soon," Musk fired back the next morning.

The Short That Started It All

The bad blood between these two billionaires isn't new. Gates confirmed in Walter Isaacson's 2023 biography of Musk that he had indeed shorted Tesla (TSLA) stock, and that Musk didn't take it well.

"Once he heard I'd shorted the stock, he was super mean to me," Gates told Isaacson. "But he's super mean to so many people, so you can't take it too personally."

For Musk, though, this was intensely personal. In a September 2023 post on X, he explained exactly why Gates' move crossed a line. "Taking out a short position against Tesla, as Gates did, results in the highest return only if a company goes bankrupt! Gates placed a massive bet on Tesla dying when our company was at one of its weakest moments several years ago," he wrote.

More Than Just a Bet

Musk didn't stop at calling out the short itself. He argued that large short positions like Gates' actively harm everyday retail investors by driving stock prices down. "Such a big short position also drives the stock down for everyday investors," Musk wrote. "To the best of my knowledge, Gates still has that massive bet against Tesla on the table."

Then came the hypocrisy charge. Musk revealed that Gates had approached him about climate philanthropy while allegedly maintaining the short position. "The lack of self-awareness and hypocrisy of Gates who had the nerve to ask me to donate to his mostly window-dressing environmental causes, while simultaneously aiming to make $500M from Tesla's demise, boggles the mind."

Unfinished Business

There's been no public confirmation from Gates that he's closed the short position. But Musk clearly believes it's still active, and the Microsoft sale gave him the perfect excuse to resurrect the feud.

The Gates Foundation's decision to sell Microsoft stock probably had nothing to do with Tesla. But when you're Elon Musk and you see Bill Gates making any kind of stock move, apparently that's reason enough to remind the world—and Gates—that some bets aren't forgotten.