Vanessa Minnillo engagement ring

Vanessa Minnillo shows off her giant engagement ring. Photo: Splash News

Some birthday presents really are the icing on the cake.

"True Beauty" host Vanessa Minnillo touched down for a Mexican vacation on Nov. 5 flashing her new engagement ring, a little pre-30th birthday bling from new fiancé Nick Lachey.

The lovebird Scorpios, who share the same Nov. 9 birthday and have been dating since 2006, announced their engagement via Lachey's Twitter account.

"If anyone's heard the rumors of my engagement they are absolutely true," the singer, who turns 37 next week, tweeted. "Vanessa and I couldn't be happier. Thanks for all the love."

The ring appears to be a whopper; a platinum-set Asscher-cut diamond with trapezoids on the side from designer Bader & Garrin, according to Us Weekly.

Jewelry expert Michael O'Connor tells the magazine that the center stone is approximately 4 carats, estimating the ring's cost at a cool $125,000.

"The platinum setting... makes this a classic ring, but the trapezoid diamonds give it a modern twist," O'Connor adds.

A source reveals to the weekly that Minnillo is very happy with the rock: "It's big and beautiful. She loves it."

This will be the first marriage for Minnillo, a former Miss Teen USA, and the second for Lachey, whose high-profile marriage to Jessica Simpson was chronicled in the MTV reality series "Newlyweds."

Speaking of Simpson, she's on the outs with an important, longtime confidant. Read about her recent parting with hairstylist Ken Paves.