Former BEATLE Sir Paul McCartney is determined to remain upbeat during his divorce battle with his estranged wife Heather Mills. The Yesterday star wants to reach an amicable agreement with Mills for the sake of their three-year-old daughter Beatrice. MCCartney says, "It's a sad thing to have happened and it's nothing that anyone wanted. "I'm not the only person in the world who's going through or has been through this kind of thing. I look for a optimistic conclusion. I'm being positive about it."