James Gunn revealed Groot's last line in Infinity War, and it is very, very sad

[The following contains major spoilers for Avengers: Infinity War and the Guardians Of The Galaxy films.]
In the Guardians of the Galaxy films (and, of course, Avengers: Infinity War) Groot is a tree with superpowers that, in lieu of conventional speech, can only utter the words “I am Groot.” That sounds very, very silly on paper, but Guardians director James Gunn has continually given us reasons to not just care about the character, but also to get kinda weepy about it.
First, there was Groot’s major sacrifice at the end of the first Guardians, which found the tree subsequently resurrected as a wee sapling named, appropriately, Baby Groot. Then Gunn made us pray for a plant heaven by informing us that, no, Groot is totally dead and Baby Groot is his son. But parentage is a slippery thing in the Guardians universe; themes of adopted families and father figures abound in the stories of Star-Lord, Gamora, and, as Gunn revealed on Twitter last night, Groot.