The rumors were true: the inventor of Twitter is officially returning to the company. Jack Dorsey, who was ousted as CEO of Twitter in 2008, will become the company's executive chairman in charge of product development. 

"Today I'm thrilled to get back to work at @Twitter" tweeted Dorsey. Shortly afterwards, Twitter CEO Dick Costolo welcomed him back saying he was "excited that Twitter Chairman @jack will be returning to the company day-to-day."

Dorsey said he'll remain CEO of Square, a mobile credit card payment startup, while assuming his new position at the microblogging site.

Clearly the company has become a more hospitable place for Dorsey, who was devastated by his public ouster three years ago. So what's changed? It could be the diminished role of the former CEO who replaced him Evan Williams. According to many accounts the two do not get along but now that Williams is rarely showing up for work (supposedly), it may have opened up more breathing room for Dorsey. Update: Yes, apparently Evan Williams has become quite detatched from the company. In a letter to TechCrunch, a Twitter spokesperson writes:

Ev decided a couple months ago to be less involved day to day at Twitter. He continues to have a close relationship with the company providing strategic advice and, of course, he remains an active board member....

Mr. Williams, meanwhile, has been spending less time in the office and long periods in Tahoe, where he is mulling a new start-up idea, according to several people with internal knowledge of the goings-on at Twitter.