Update: According to the film's director, definitely not.
UPDATE: James Gunn responded to fans on Twitter regarding the Bradley Cooper interview to affirm that Cooper was not revealing Thanos as Peter Quill’s father, and that even at the time of the interview he was unaware of who the villain for Guardians of the Galaxy Vol. 2 was. As suggested below, it sounds like Cooper was misremembering scenes from the first film featuring Thanos, Ronan, and Nebula, along with the mystery of Quill’s father being such a major thread hanging after the original film.
See Gunn’s responses (according to him, Cooper has just gotten the sequel’s script) and the original interview below.
Original Story: Speaking in a recent interview for Burnt, Bradley Cooper, the voice of Rocket Raccoon, may have inadvertently revealed a major mystery surrounding Chris Pratt’s Peter Quill going into Guardians of the Galaxy Vol. 2. Or he just has trouble remembering what happened in the first film.
“[Josh Brolin] is the main villain, no? He was in the first one, he played what’s his name’s dad… Dark Lord, the main guy,” Cooper told MTV International about Brolin’s character, Thanos. When the interviewer tells him the audience doesn’t yet know who “the main guy’s” father is, Cooper seems to reaffirm that Thanos is someone’s father, thinking a scene in the first movie revealed that. His Burnt co-star Sienna Miller seemed to be more aware of the possible secrecy breach, giggling and saying, “Oops … you just leaked a Marvel script, Bradley.”
Now, there are two possible explanations for what he said. He either inadvertently revealed Thanos as Peter Quill’s father, or conflated a few characters and a scene from the first film. Cooper describes a scene in which Thanos turns around in his chair and speaks to his son, which is not unlike the scene from the first Guardians in which Thanos speaks to his daughter, Nebula, and the film’s other villain, Ronan the Accuser. Cooper did describe a sister being involved in the scene, as well.
The mystery of Quill’s father was one of the lingering questions that came out of Guardians of the Galaxy (and one director James Gunn has discussed he already has mapped out), as Gunn has explained it will not be who Quill’s father is in the comics.
Cooper does seem confident that Thanos is the main villain of Guardians of the Galaxy Vol. 2 (even if he can’t quite remember the character’s name), so whether he accidentally shared a major plot point or not, he at least appears aware of Thanos’ continued presence in the series.
Marvel did not immediately respond to a request for comment.