Levi Johnston & Bristol Palin: No Sex Until Marriage!

Most of the time, when a couple vows to stay abstinent until marriage, the dude hasn't already knocked up the girl, broken up with her, trashed her mom in the media, posed nude in Playgirl, then rekindled the romance during custody negotiations.

But hey, whatever works for Levi Johnston and Bristol Palin!

America's favorite unwed teen mom and her once-estranged baby daddy surprised us by getting back together last month, then flat-out floored us with news that they are now engaged, and planning on tying the knot soon.

Like real soon. By the end of August!

Levi, Bristol Photo

Levi and Bristol say they hope to get married within the next six weeks, and due to her abstinence pledge, won't be having sex again until after they say "I do."

No word if there will be protection involved at that time, or if they simply don't believe in that. Tripp is really cute, he'd probably be an awesome big brother.

The best part, aside from the abstinence thing, is that they say they didn't tell her mom, Republican political heavyweight Sarah Palin, about the engagement.

Instead, they told Us Weekly, who broke the story earlier this morning, hoping that it was one of the "variety of sources" the former Alaska Governor reads.

As for the wedding, they'll be getting married in Alaska, natch. According to sources, she wants Levi to wear a camouflage vest, too. That may not be a joke.

Regarding those nude Playgirl photos that sparked so much controversy ... Bristol Palin claims she hasn't seen them and chalks it up to "Levi's old life."

It ran in February. Just saying. (thehollywoodgossip)