According to the publication's source, Jen was shocked when Brad wrote, "I never stopped loving you," while confessing that he had thought about her "every single day since their split".
"After that he made a promise that changed everything. He told her that if she were to take him back he would do everything to prove that he's a changed man," the insider continued.
"He then apologised for humiliating her and swore he'd never hurt her again."
The publication's source goes on to claim that Brad has won Jen's heart all over again.
"This is the nice Brad she fell in love with all those years ago. Jen's telling friends it's wonderful to see him back."
Brad and Jen have yet to comment on OK! magazine's claims.