Ironically, not only do the newly engaged share an adoration for each other, but they also share the same birthday, which this Tuesday.
"They are [in Mexico] to celebrate their engagement and their upcoming birthdays," a source tells PEOPLE. "They are having a great time together and enjoying their special moment."
Minnillo, pictured holding a balloon that shows she is turning the big 3-0, is also sporting her new ring. Lachey will turn 37.
– Dahvi Shira and Liz McNeil