Bristol Palin's former fiance is talking about their sex life on TV. Levi Johnston, 18, father of son Tripp with Bristol, told The Tyra Banks Show he practiced safe sex "most of the time" while with Bristol. He also reported that Alaska Gov. Sarah Palin knew he and Bristol were sexually involved. "I'm pretty sure she probably knew. Moms are pretty smart," Johnson said. The two were planning to wed after graduating, but ended up separating earlier this year. (Photo: WENN)