Billionaire investor Peter Thiel just joined startup incubator Y Combinator

Billionaire investor Peter Thiel has officially joined startup incubator Y Combinator strictly as an advisor, not as an investor.

"I'm delighted to announce Peter Thiel is joining YC as one of the (now 10!) part-time partners," Y Combinator CEO Sam Altman wrote on its blog, adding that Thiel was already working with a number of Y Combinator companies.

"On a personal note, Peter is one of the two people (along with PG) who has taught me the most about how to invest in startups. I am confident that Peter joining will be great for YC," Altman added.

Y Combinator is an incubator where early stage startups receive seed investment, advice and connections from its experienced partners. Some of its full-time partners include Y Combinator founder Paul Graham, Justin.tv and TwitchTV cofounder Justin Kan, and Reddit founder Alexis Ohanian.

Other part-time partners include the likes of Groupon founder Andrew Mason, Stripe cofounder Patrick Collison, and Homejoy founder Adora Cheung.

Altman added in the blog post that in order to prevent any type of conflict of interest, Thiel won't be investing in any of the companies while they are in Y Combinator or for the three months after presenting at Demo Day, YC's big pitching event that happens twice a year.

Thiel runs a number of different investment firms, including the Founders Fund and Mithril Capital, as well as his own startup fellowship program called the Thiel Fellowship.

Today's news comes at an interesting time. Last week, Business Insider's Jonathan Marino reported that YC is close to raising several billion dollars for a new fund, with the goal of possibly expanding its scope to later stage funding. It said it's still in preliminary discussions for this new strategy, but if true, Thiel could definitely play a big role there.