No official announcement from Marvel Studios or parent company Disney has made it official, yet it’s all but confirmed that Vin Diesel is in fact, playing Groot in Guardians of the Galaxy. Since before San Diego Comic-Con in July, the star of the Fast & Furious franchise has been teasing the idea voicing the fifth and largest member of the Guardians, revealing in the following months how the possibility came to be.

Initially Marvel had met with Diesel to talk about a lead part in a Marvel superhero film that wouldn’t come to theaters until 2016-17, a “new IP” as he describes it, but the response on his Facebook page – which currently has nearly 49 million fans – demanded something sooner. Guardians director James Gunn and Marvel Studios boss Kevin Feige came up with an idea for something that could fit Diesel’s currently busy schedule, while still planning to work together down the road on that other unannounced movie.

Up until recently however, seemingly no deal had been made and Diesel had not signed on for the role, despite his interest (and that of his kids) for him taking the part. What interests Diesel most about the character of Groot is how unique of a challenge it is for him as an actor, and it would be the first time where he could do work similar to Andy Serkis’ award-worthy motion capture performances in Lord of the Rings and Rise of the Planet of the Apes.

Last night, Diesel posted to his wall a video from the set of Fast & Furious 7 where on his downtime, he’s practicing walking around on stilts to make him 7-feet tall, preparing for what will be his motion capture work for Groot, likely to begin as soon as FF7 production wraps. Guardians of the Galaxy finished shooting last week so Gunn and crew need to get to work soon on motion capturing scenes where they need an actor to play Groot and as for the dialogue of the character, Diesel confirmed what we expected in that the character has only one line of dialogue (“I am Groot!”) that he uses in any and all conversations, just with different tones. This represents two unique challenges for Diesel bringing the animated character to life physically and through sound.

The video offers a great behind-the-scenes look into how Diesel has fun on set and is excited about joining the Marvel Cinematic Universe. There’s also a special guest appearance from Fast & Furious 7/Guardians of the Galaxy co-star Djimon Hounsou. If anything, at least Diesel is helping give Marvel and Disney plenty of free marketing for Guardians. And look, he seems to have gotten the mobility part down. Groot will be sharing much of his screentime with the other animated member of the Guardians of the Galaxy, Rocket Raccoon, who will be voiced by Bradley Cooper.

Groot & Rocket Racoon

Will Marvel.com make the Vin Diesel announcement soon?

Guardians of the Galaxy is directed by James Gunn off of his script co-written by Nicole Perlman. Cooper 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.

Thor: The Dark World on November 8, 2013, Captain America: The Winter Soldier on 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.

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Source: Vin Diesel