Hugh Hefner gave his #1 girlfriend Crystal Harris an engagement ring for Christmas -- and now we've got your first look at the gorgeous gift!

Last night on her Twitter, Crystal posted "For those of you who have been asking to see my ring here it is... My engagement ring from my love @hughhefner" -- and linked to this photo of some serious sparkle.

Hugh popped the question on Christmas Eve, with the Playboy founder tweeting after "When I gave Crystal the ring, she burst into tears. This is the happiest Christmas weekend in memory."

As for Hef's famous exes, Kendra Wilkinson tweeted "so happy for you" at the couple while Bridget Marquardt sent over a note and a box of "I Do" cupcakes from Sprinkles.

No word yet from Holly Madison -- but she and Hugh are set to shoot an episode of "Holly's World" at the Mansion together next week.