Spencer Pratt and Heidi Montag are engaged!

Pratt, 23, popped the question to Montag, 20, Tuesday night at the Bacara Resort & Spa in Santa Barbara, says a source who adds: "She said 'yes.' She's over the moon!" The Hills stars, whose controversial courtship was chronicled last season on the hit MTV reality series, have been dating for just eight months.

Pratt purchased the diamond-encrusted platinum band with a pink stone on Monday at Ice at Brentwood Gardens before presenting Montag with his bended-knee proposal, according to a source. An eyewitness at the store tells Us, "She was trying on tons of them and they looked really happy!"

Montag was formerly a close friend and roommate of her Hills co-star Lauren Conrad, 21, until Pratt earlier this year urged Montag to move out of Conrad's apartment and in with him. The couple has not yet set a wedding date. A rep for MTV couldn't be reached for comment.

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