Tyra Banks grills Levi Johnston, the former boyfriend of Bristol Palin, on Monday’s edition of The Tyra Banks Show. Joined by his mother and sister, the 18-year-old father of Governor Sarah Palin’s grandson is opening up about the circumstances surrounding his son’s conception.

In the interview, Tyra asks Levi, “Did [Sarah Palin] think you were abstinent?” and Levi responds, “No.”

Levi, who was sharing a room with Bristol in the Palin residence prior to their breakup earlier this year, tells Tyra he believes the Alaska governor–a devoted proponent of abstinence-only education, knew the teens were having sex.

“I’m pretty sure she probably knew. Moms are pretty smart.”

When Tyra asks Levi whether he and Bristol were “practicing safe sex,” he responded, “Yeah,” but admitted later that it was only “most of the time.”

Bristol gave birth to the couple’s son, Trip Easton Mitchell Johnston, in December.

For the full interview with Levi Johnston, tune in to Monday’s Tyra.