For months now, Vin Diesel has talked up his excitement, research and training for the role of Groot in Marvel’s upcoming space epic Guardians of the Galaxy. Diesel is not only voicing the largest of the Guardians team, a walking, sentient tree who speaks only in the words “I am Groot!” but he’s doing some of the motion capture as well.

Despite the frequency of news relating to him having the part, even co-stars talking about his talents, it was never officially official. Much like Marvel announcing the casting of Aaron Taylor-Johnson and Elizabeth Olsen in The Avengers: Age of Ultron, Diesel being officially added to the roster of stars in Guardians of the Galaxy comes as absolutely no surprise.

We had heard from Marvel Studios president of production Kevin Feige that official announcements regarding new cast members in The Avengers 2, Ant-Man and Guardians of the Galaxy would be coming by the end of the year and that promise was held. In addition to Taylor-Johnson and Olsen joining Age of Ultron as Quicksilver and Scarlet Witch, respectively, funnyman Paul Rudd was officially cast this week as Ant-Man in Edgar Wright’s long-in-development Marvel movie. Joining them in the Marvel Cinematic Universe will be Vin Diesel as the alien known as Groot.

Guardians of the Galaxy director James Gunn took to Diesel’s favorite social media platform, Facebook, to confirm the news with the photo up top earlier today (just before Marvel posted it on their official site), where Diesel has his arm around a bust of the character he’s playing. Gunn notes that there have been a few tweaks to the Groot design throughout the process and what’s shown above is what the character will look like in the film.

“Vin Diesel is a super awesome dude. I can’t tell you how much I like this guy. “

While responding to Facebook comments, Gunn elaborated and clarified a few things – namely, that despite all the talk and reports of Diesel’s involvement – mostly from the star himself – he was never actually signed for the part, just interested and in talks. Now he’s on board and has already begun his recording sessions.

“He was never announced. He said he wanted to do it and we said we were talking to him. Everything else was people guessing and thinking they knew what was going to happen.”

“Also I hope this puts to rest all the silly Thanos-Vin stuff which people just seemed to make up out of nothing.”

Note the second part where he addresses the rumors that Marvel and Gunn may have been planning a bait-and-switch, making fans think Diesel’s only coming in for Groot, but actually playing (or also playing) the big bad villain known as Thanos – the alien dude at the end of The Avengers who smiles at the idea of “death.” Still, we know Vin Diesel initially met with Marvel to talk about another, much larger role coming in 2016-17 and that’s still on the table. It’s a part that Diesel hints will “merge brands” and one of our more obvious theories is that he could be leading a movie based on another team of powered heroes called The Inhumans.

So, who’s playing Thanos?

Guardians of the Galaxy is directed by James Gunn off of his script co-written by Nicole Perlman. Diesel joins a cast led by Chris Pratt, Zoe Saldana, Dave Bautista, Lee Pace, Michael Rooker Karen Gillan, Djimon Hounsou, Benicio del Toro, John C. Reilly, Bradley Cooper and Glenn Close.

Captain America: The Winter Soldier hits theaters April 4, 2014, Guardians of the Galaxy on August 1, 2014The Avengers: Age of Ultron on May 1, 2015, Ant-Man on July 31, 2015, and unannounced films for May 6 2016, July 8 2016 and May 5 2017.

Follow Rob on Twitter @rob_keyes for your Marvel movie news!

Sources: James Gunn (Hat-tip to Nicholas), Marvel