We all bid a tearful goodbye to Groot in Guardians of the Galaxy, though the sentient tree found new life when Rocket potted a twig that eventually returned as Baby Groot. According to James Gunn, they're two separate beings, and we've since been able to watch this Groot mature in the Avengers movies (as a teen) and then as a young adult in The Guardians of the Galaxy Holiday Special.
In Guardians of the Galaxy Vol. 3, he's pretty much an adult and has mastered his abilities in a way not even his predecessor did.
For example, he at one point goes into "Kaiju-mode" by expanding his body to make himself giant-sized, while also surviving an earlier battle with Adam Warlock by being little more than a head with some roots coming out of his neck (from there, he grows his body back surprisingly quickly).
However, Gunn saves the biggest Groot surprise for last.
When the team decides to go their separate ways, we hear Groot, who is still voiced by Vin Diesel, tell them, "I love you guys." Now, this is likely to be a hot topic of debate among fans; is Gunn simply allowing us to understand the character for the first time in order to make this scene even more emotional or has Groot somehow developed the ability to speak English? If we were putting money on it, it would be the former.
This isn't the only shock, however, as the mid-credits scene - which showcases the new Guardians of the Galaxy - introduced Groot's latest form.
Now looking more akin to King Groot from the Marvel: Contest of Champions video game, he's clearly reached his ultimate potential and is likely the most powerful version of himself yet. Gunn also appears to have pulled some inspiration from the character's first Marvel Comics appearance, and in terms of sheer size, he's now up there with The Hulk and Thanos (and perhaps even larger).
We don't know when Groot and his fellow Guardians will return, but fingers crossed we're not waiting too long.
Guardians of the Galaxy Vol. 3 is now playing in theaters.