Bristol Palin and Levi Johnston announce in the new Us Weekly that they're engaged -- and in this exclusive video, they reveal how he popped question.

Watch Levi, 20, turn red as Bristol, 19, teases him about his romantic proposal two weeks ago at her condo in Anchorage, Alaska.

Levi -- whose relationship with the Palin family had been strained since he and Bristol called off their first engagement last year -- also vows that he will now be there for his 18-month-old son.

"I've missed out on a lot of his life, and I can't get that back," he tells Us in the video. "Seeing him walk or crawl for the first time, or his first word ... I missed all that. More importantly, I am here now, and I am going to make it right." Says Bristol, "It just feels right to be family."

To read the whole interview, pick up the new Us Weekly today!