More than four months ago, outspoken cutoff sleeve advocate Diesel let the space-cat out of the astro-bag, revealing that he would be voicing the alien tree-creature that serves as muscle on the titular team and whose dialogue consists exclusively of "I AM GROOT."

Since then, it's been common knowledge.  Chris Pratt, who stars as half-Earthling, half-alien rogue Peter Quill aka Star-Lord, even talked exclusively to IAR about it, saying, "Dude, I think Vin Diesel is going to be great. The role of Groot is also an amazing role. I want to tell you about it but I feel like if I tell you even one little thing it's going to start pulling the thread that is going to expose too much."

Still, neither Marvel nor director/co-writer James Gunn have been willing to make it official.  Until now, with Marvel announcing it (the press release is included below) and Gunn taking to Twitter to declare "Vin Diesel is a super awesome dude. I can't tell you how much I like this guy."

Stand-up guy Gunn also shared the below image, giving a good look at Diesel and a bust of good old Groot:

So, just to clear up exactly how strange Guardians of the Galaxy is: Vin Diesel and Bradley Cooper are voicing, respectively, a talking tree and a talking raccoon.  In a movie from the guy who wrote and directed the beautifully repulsive Slither and the aggressively odd Super.  Oh, and rounding out Star-Lord's team is Zoe Saldana playing a green-skinned intergalactic assassin Gamora and Diesel's Riddick co-star Dave Bautista as dead-jazz-musician-turned-alien-badass Drax the Destroyer.

All that would be weirdness enough for five or six other movies, but Gunn and Marvel aren't done there.  Nope, the cast here also includes Benicio Del Toro, Lee Pace, Glenn Close, Karen Gillan, Djimon Hounsou, Michael Rooker, and Peter Serafinowicz.

Guardians of the Galaxy brings Groot and the rest of the team to theaters on August 1, 2014.

Here's the announcement on Diesel:

Vin Diesel is Groot!The star of the Fast and the Furious and Riddick franchises will lend his voice to Groot in Marvel’s live-action “Guardians of the Galaxy,” rounding out the team that includes Star-Lord (Chris Pratt), Rocket Raccoon (Bradley Cooper), Gamora (Zoe Saldana) and Drax (Dave Bautista). Featured in four of the six movies in the fan-favorite “Fast & Furious” franchise, Diesel has helped the series gross over $2 billion at the box office; and will reprise his role in “Fast & Furious 7.” Diesel’s most recent film, “Riddick,” the third film in the franchise that has so far earned a cumulative $267.3 million across the globe, debuted this year at the top of the box office. In addition to lending his voice to several video games, Diesel’s received great acclaim for his voice work in the celebrated animated film “The Iron Giant,” directed by Brad Bird. In the far reaches of the Marvel Cinematic Universe, an unlikely cast of characters including Peter Quill, Gamora, Drax, Groot and Rocket Raccoon must join forces to defeat a cosmic force of epic proportions. Directed by James Gunn, the live-action “Guardians of the Galaxy” will take fans to new corners of the Marvel Universe when it hits theaters August 1, 2014, but in the meantime stay tuned to Marvel.com for the latest news as it breaks, including official casting, first looks and more!