Peter Thiel (left) and Elon Musk (right) during the early days of PayPal. AP Way back in 1999, Elon Musk started X.com, his second-ever company.

It was an online bank that would go on to become PayPal. In 2001, he stepped aside, leaving behind both X.com the company and X.com the domain name.

Now, over 16 years later, Musk and X.com are back together: PayPal confirms with Business Insider that Elon Musk has repurchased the X.com domain name. The news was first reported by Domain Investing.

"We are delighted to sell the domain x.com back to its previous owner, Elon Musk," says a PayPal spokesperson.

To be clear, he hasn't purchased PayPal, or even a sliver of PayPal. All he purchased was X.com, a highly-desirable single-letter website address, and he can now do whatever he wants with it.

PayPal didn't disclose how much Musk paid for the X.com domain name. Right now, there's nothing so much as a placeholder at X.com.

Maybe this is just for nostalgia. Maybe Musk has plans to start a new company using a classic name. Or maybe he could use it to promote one SpaceX, his space-faring company, or Tesla's Model X SUV.

We don't know. What we do know is that Musk — the founder of Tesla, SpaceX, OpenAI, and the Boring Company — rarely sits still for very long.

"I guess you can say that I'm a serial entrepreneur," Musk said when he left X.com in 2001.

Later on Monday night, Musk officially shared the news that he had repurchased X.com, saying that he had no immediate plans for the domain name, but that "it has great sentimental value to me."