The two billionaires switched ranks earlier this month, when Zuckerberg, 39, overtook Musk for the first time since 2020 following news that Tesla’s vehicle deliveries fell in the three months through March.

Shares of Menlo Park, California-based Meta fell Thursday by the most since October 2022 after the company increased spending estimates for the year and projected second-quarter sales that were below Wall Street’s expectations, once again raising questions about whether its bets on artificial intelligence will eventually pay off for investors.

Read More: Zuckerberg Asks for Patience as Meta’s AI Push Spooks Investors

The stock is still up 22% for the year and has been trading near all-time highs for the past month, in part reflecting excitement around AI.

Shares of Austin-based Tesla surged 12% on Wednesday after Musk vowed to offer less-expensive vehicles as soon as this year, easing concerns about disappointing earnings results and diminished growth prospects. The stock was the worst performer on the S&P 500 Index before the rally, falling 42% through Tuesday’s close.

Read More: Tesla Soars as Musk’s Cheaper EVs Calm Fears Over Strategy

Musk derives his wealth primarily from his stake in the EV manufacturer, as well as his holdings in Space Exploration Technologies and X, formerly known as Twitter. Zuckerberg’s fortune is largely tied to Meta shares.

The two billionaires’ rivalry extends beyond their wealth: Musk and Zuckerberg have been engaged in an ongoing public spat that intensified when Meta launched Threads, a social-media platform that competes with Musk’s X. The two even traded barbs last year about a possible cage fight.