Actor Jennifer Aniston has got an offer to release a tell-all book with details of the past and the news is reportedly making Angelina Jolie nervous.Aniston's ex-husband Brad Pitt and Jolie are now partners.Jolie and Pitt grew close to each other while filming the 2005 film Mr & Mrs Smith, during which time the latter was married to Aniston."Angelina's worked hard to build up her image as a humanitarian and separate herself from the public outcry when she got together with Brad. She felt the whole 'Team Jen' and 'Team Ange' thing had finally died a death and that the perception of her being a husband stealer was in the past, but then she heard about the book offer," a source told Now magazine, reports contactmusic.com.Aniston, now engaged to Justin Theroux, knows that the part where she will recount the deatils of her break-up with Pitt will be tough to write, said the source."If Jen does sign a book deal, she knows the chapter on Brad and Ange will be the hardest for her to write - but it will also be the one everyone will be after. Jen doesn't want to spark any new rows, but there's so much history involved that it's inevitable," the source added.