Bristol's Engaged!

Just like her parents before her, Bristol Palin is set to marry her high school sweetheart.

OK! has learned that Bristol, 17, and her boyfriend, Levi Johnston, 18, who are expecting their first child together, are officially engaged!

“Bristol came in mid-July to have her engagement ring sized down,” Brian Johnson, manager of Alaskan Gold Rush Jewelers in Wasilla, Alaska, tells OK! exclusively. “It’s a 3/4-carat princess-cut solitaire diamond with a white-gold, square-edged band. It’s perfect for a young couple.”

Those who know the pair are rallying around them, saying they are ready for the future.

Although Levi said on his MySpace page, “I don’t want kids,” Todd Wohlers, the father of Trent Wohlers, a hockey teammate of Levi, tells OK!, “He’s going to step up to the plate and do what’s right.”

Adds Levi’s friend Ilsa Schwarzburg, “He’ll get married, if that’s what she wants to do.”