Twitter co-founder Jack Dorsey is betting that Elon Musk can turn the social platform’s fortunes around.

According to securities filings Monday evening, Dorsey opted to roll his ownership stake in the company over to Musk’s new private venture. While Musk had said in the months leading up to the closing of the deal that he had been in talks with Dorsey to roll over his stake, neither man had confirmed the deal until the filings were disclosed on Oct. 31.

Dorsey owned more than 18 million shares in Twitter, valued at about $1 billion. He could have cashed those shares out at $54.20 a piece when Musk took the company private, instead, he will end up saving Musk about $1 billion in his purchase price by rolling those shares over.

The rollover keeps Dorsey around as one of Twitter’s largest shareholders, after only Musk and Saudi Arabia’s Prince Alwaleed Bin Talal, who rolled over about $1.9 billion worth of Twitter stock into Musk’s private venture. 

Dorsey and Musk are friends, with the Twitter co-founder having endorsed Musk’s takeover effort.

“Elon’s goal of creating a platform that is ‘maximally trusted and broadly inclusive’ is the right one,” he tweeted after Musk launched his takeover. “This is also [Twitter CEO Parag Agrawal’s] goal, and why I chose him. Thank you both for getting the company out of an impossible situation. This is the right path. … I believe it with all my heart.” 

While Agrawal was close to Dorsey, he did not share that connection with Musk, who fired him for cause after closing the Twitter deal. It is not immediately clear what cause Musk terminated Agrawal for, or if the former CEO will seek to take Musk or the company to arbitration over the decision.