There's no love lost between Levi Johnston's little sister and his ex-fiancee Bristol Palin.
19-year-old Alaskan Mercede Johnston poses nude in the September issue of Playboy -- and rips into her older brother's would-be in-laws, Alaska's most famous political family, in a shocking interview.
"Everything is about her, her, her," Johnston says of Bristol, 20, who has a 2-year-old old son, Tripp, with former fiance Levi, 21.
"She has to have her own way. She'll be supersweet and then she turns into the most evil person I've ever known . . . Honestly, she is the meanest person. I didn't know someone could be so vindictive and evil …[She's] a sociopath. She doesn't think anything she could do or does is wrong."
Although much was made of Bristol's surprise pregnancy at age 18, Mercede tells Playboy that Tripp's arrival wasn't that much of a shock to her. "Bristol's pregnancy wasn't unexpected, an accident. She and Levi planned it. They were trying to conceive for months."
She also sniped about Levi and Bristol's relationship. "Levi was whipped like Todd [Palin], because Bristol is very manipulative. She'd use sex to get her way on many things."
Despite their nasty fights, Johnston claims she's attempted to make amends -- but in vain. "She'll just say, 'F you. Don't contact me ever again.'"
"The truth about the Palins will come out," Mercede warns.The new issue of Playboy hits stands Aug. 12.