Twitter co-founder Biz Stone is returning to Twitter

Twitter co-founder Biz Stone is rejoining the company.

Stone, who left Twitter in 2011 and recently sold his startup Jelly to Pinterest, announced in a blog post Tuesday that he’s headed back full-time to the company he helped found.

It’s not exactly clear what Stone’s title will be, but a source familiar with the move says he’ll report to Twitter CMO Leslie Berland and help with internal communications and morale at the company.

Stone has always been a positive, rah-rah kind of executive. He was responsible for helping promote Twitter to the press and to celebrities in the company’s early days. It sounds like he’s trying to recreate some kind of spark that Twitter may have lost over what’s been a tough couple of years.

“My top focus will be to guide the company culture, that energy, that feeling,” Stone wrote. “It’s important that everyone understands the whole story of Twitter and each of our roles in that story. I’ll shape the experience internally so it’s also be felt outside the company.”

Stone says he’s returning “full time,” which we assume means he won’t work part-time at Pinterest as an adviser, as was the plan earlier this year when Pinterest acquired his startup. We’ve reached out to Pinterest for clarification and will update when we hear back.

Update: A Pinterest spokesperson told us that Stone will continue to serve as an advisor to co-founder and product boss Evan Sharp even with his new full-time role at Twitter.

In the meantime, Twitter now has two of its co-founders back in the building every day, with a third, Ev Williams, sitting on the board.

According to Stone’s blog post, his decision to re-up was surprising, even to him. CEO Jack Dorsey apparently asked him to return while Stone was visiting at the company’s all-hands gathering, called Tea Time, a few weeks back.

“I wasn’t really sure if he meant it,” Stone wrote. “After Tea Time, we spoke privately and Jack told me that he really did — he wanted me to come back and work at Twitter. The company I co-founded, the service I co-invented. I was stunned, but I knew the answer.”

Stone and Dorsey have maintained a close relationship since founding the company together. The duo used to catch up weekly over tacos in San Francisco and are still close friends. And now, apparently, co-workers once again.

This article originally appeared on Recode.net.