As moviegoers already know, Natalie Portman's Jane Foster isn't a part of Thor: Ragnarok. While her absence is likely due to contracts rather than narrative choice, fans at least now know the in-story reason we'll no longer see her: unsurprisingly, she and Thor broke up. Entertainment Weekly reports that the couple broke it off in an off-camera moment following Thor: The Dark World, with Thor himself Chris Hemsworth explaining that he’s “a solo cowboy.” Assumingly this was done as a way to write Portman's character out of the movie.
“He’s off exploring the universe, still trying to police it and control the mayhem,” said Hemsworth. “But he’s certainly enjoying being a drifter, being a solo cowboy out there.”
Portman was quoted in 2016 saying that she hadn’t been contacted by Marvel to appear in Thor: Ragnarok, something the other major female character from the Thor movies, Jamie Alexander (who played Sif), echoed. It's unknown if they had more films in thier respective deals with Marvel Studios, but in some cases Marvel Studios has let actor's multi-film contracts lapse.
Feige had peviously said that Portman's absence would be addressed during Thor: Ragnarok.
Thor: Ragnarok will introduce a new character, Valkyrie (played by Tessa Thompson), that Marvel Studio President Kevin Feige said is intended to be “near his equal.”
“We wanted Thor to encounter somebody that was near his equal and that his relationship with Jane may have evolved in unexpected ways in between The Dark World and Thor: Ragnarok and we wanted to pit him against a character who was much more his equal and in many ways his superior. Valkyrie is trying to not embrace any sort of Asgardian heritage that she has. Thor thinks maybe that will create a bond between them and, on the contrary, she wants to forget it all entirely.”
Interestingly, this would be second Marvel Cinematic Universe power couple to fizzle – during Captain America: Civil War, Robert Downey Jr.’s Tony Stark said that he and Pepper Potts had taken a break from their relationship.
Thor: Ragnarok is scheduled to be released in theaters November 3.