Levi Johnston, ex-fiancee of famous teen mom Bristol Palin, admitted to Tyra Banks in an interview set to air Monday that the couple was not always practicing safe sex and says they shared a bedroom on occasion. Johnston talks about his relationship with Sarah Palin's daughter next Monday on "The Tyra Banks Show." In a preview, Johnston tells the host that he and Bristol were practicing safe sex, and agrees that her pregnancy must have resulted from some sort of 'wardrobe malfunction.' But when pressed by Tyra, he admits that they used protection "most of the time" -- but not all the time. According to the show's website, Johnston also dishes to Tyra about being thrust into the spotlight at the Republican National Convention, and why his engagement with Bristol ended, what he really thinks of Governor Palin and what it's like to be a teen father. People has some additional quotes, including that he believes Sarah Palin knew he and Bristol were sexually active, as they shared a bedroom. "I'm pretty sure she probably knew," says Johnston. "Moms are pretty smart." He also shows off his ring-finger tattoo to Tyra. Watch Johnston discuss safe sex here. In a recent interview with "Good Morning America," Johnston said he and Bristol needed time to "mature" but could reunite in the future.