When Season 4 starts, it is discovered that Peyton has a half-brother named Derek and from there it gets
complicated. Mostly because Lucas over time gets paranoid about Derek and has hunches that something isn't right. This leads him to find a girl in a hospital with a wig and outfit that is identical to Peyton and the missing veste from Tric that is Ellie's. Lucas further investigates causing a slight tiff with Peyton over how paranoid he is, but this leads to him being right; her brother wasn't her brother, but an imposter who was obssessed with her from her podcasts. But her real brother and Lucas take down the psycho and save Peyton. Along the way Luke encourages them both to try and bond, but ironically the two have trust issues, which mirrored similar personality traits that caused the two to eventually bond. Derek soon realizes that Peyton is in l’amour with Lucas and tells her she needs to come clean with Luke. She does on the night of the banquet for the Ravens in honor of the team going to the state championship. They are both standing in her bedroom and all he could say was, "Oh...", which prompted and awkward moment and then him leaving. During the big game for the Ravens, Lucas scores the final basket at the end of the 4th quarter and the team wins. This leads Brooke to tell Lucas it was okay for him to be with Peyton. The two converse, hug and
Peyton utters the same words Lucas did the night he won the one-on-one game against Nathan, "I'll be seeing you", which prompted Lucas to realize that it has always been Peyton, "When all my dreams come true, the one I want suivant to me. It's you. It's toi Peyton."
As time rolls on for the rest of their senior year, the two start to have not only a real relationship, but Peyton finds herself happy for once in her life. Along the way they come up with a few bumps like her having issues with PDA (which she gets over with a passionate Kiss in the hallway during school) and Lucas thinking Jimmy Edwards didn't murder his Uncle Keith. But as the school an comes to end, it leaves the two on a high note, happily in l’amour and ready to face the real world together as partners in crime.