He was looking pretty beefy there for a while, but it seems like Rob Pattinson is struggling to keep on the muscle he's put on over the summer for his upcoming role as a military interrogator in Mission Blacklist.

X17 photographers caught Rob at the gym on Sunday afternoon, and the British hunk sported his signature scruff and quickly headed inside to get started with his cardio sesh. Here's to hoping there's some shirtless scenes in the film? For all the hard work he's putting in, it seems like there should be!

And it looks like the brunette pictured above is Rob's personal trainer Sydney Liebes ... though apparently the Twilight star has been reuniting with ex-girlfriend Kristen Stewart on the sly. Are they or aren't they back together?! So many questions...