Biz Stone, one of the co-founders of Twitter, just announced that he’s returning to the company he helped start. Stone left Twitter in 2011 to pursue new projects with Obvious Corporation, a venture that also included fellow Twitter co-founder Ev Williams.

While he was somewhat vague about what exactly his new role will be, Stone explained that his top focus will be guiding company culture. He also clarified that he’s not replacing anyone at the company:

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 felt outside the company . – Biz Stone

About a month ago Stone sold his most recent startup, Jelly, to Pinterest. He said at the time that he wasn’t required to stay on with Pinterest, so was available for new opportunities.

Stone said he was recently back at Twitter as a “special guest” for an event open to employees, where current CEO and fellow co-founder Jack Dorsey — another founder who left and then returned — asked him onstage if he wanted to come back and work at Twitter. After some employee cheers, and a private clarification that Jack was in fact being serious, he accepted.

Twitter diehards are reacting positively to the news — many think that Twitter needs to get back to its roots, and what better way to do it than bringing back a co-founder? The market also seems to be happy. TWTR stock immediately jumped 2 percent on the news, reaching a three-month high of $19.62.

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