Judging by the brilliant bauble he bought Sofia Vergara, Nick Loeb has exquisite taste.

While celebrating her 40th birthday with 90 pals at a resort in Mexico, the Modern Family star's on-and-off love of four years proposed with a dazzling diamond ring. "He was looking for engagement rings last week," a source tells Us Weekly. "He looked at a bunch of places."

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Though the pair broke up for several weeks in May, an insider hinted they would likely "get back together. They run hot and cold."

With a wedding in the works, Vergara and entrepreneur Loeb, 36, are happily celebrating their future with the actress' costars Julie Bowen, 42, Jesse Tyler Ferguson, 36, and Sarah Hyland, 21, according to a second insider. "They are all there with their significant others. Everyone is having a blast."

Hyland certainly agrees. "Who's the most wonderful, generous, beautiful woman in the world?" she tweeted July 9. "Why Sofia Vergara, of course!"

This will be the second marriage for Vergara, who was married to Joe Gonzalez as a teen; they divorced in 1993 and share a son, Manolo, 20.

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Prior to Loeb's proposal, "Sofia, her son, Manolo, and his girlfriend and Nick toured the ports. They met the governor of the state and did a lot of historic sight-seeing," the insider tells Us of their fun-filled getaway. "All of the family has been really cordial to Nick."

This article originally appeared on Usmagazine.com: See Sofia Vergara's Giant Engagement Ring From Nick Loeb!