"Yellowstone" season 5’s premiere dropped the revelation that John Dutton died by suicide. His family immediately suspected foul play, and they were correct.
John was actually assassinated, and Beth Dutton believes that her adopted brother Jamie was behind it and vows to kill her sibling, which she does in the finale.
While Jamie wasn't directly behind John's assassination, his lover, Sarah Atwood, arranged the hit job and he accepted it because his career is more important than family.
After Beth stabs him, Rip Wheeler and Lloyd Pierce dump Jamie’s body in the "train station" with all of the other corpses, possibly setting up Rip and Beth’s spin-off series.