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On Thursday, newly engaged couple Nick Lachey and Vanessa Minnillo touched down in Mexico for a pre-birthday celebration. (They both have birthdays Nov. 9: Lachey's 37th and Minnillo's 30th).

Bride-to-be Minnillo flashed a brand-new accessory for the trip: her engagement ring!

A source close to the couple tells that the piece is a platinum, asscher cut diamond with trapezoids on the side from designer Bader & Garrin. "It's big and beautiful," says the source. "She loves it."

Reps for both stars told Us exclusively about the couple's engagement on Thursday. "We're excited and incredibly happy about our engagement and we look forward to a wonderful future together," the couple of over four years told Us in a statement.

It's the first marriage for True Beauty star Minnillo; singer Lachey divorced Jessica Simpson back in 2006.