He carefully planned the proposal, which took place over Christmas in Kauai. "This wasn't spontaneous," a source close to the couple tells PEOPLE.
The couple were guests at the tony St. Regis Hotel in Princeville – an ultra-exclusive, five-star getaway for the rich and famous – and the source says that "Joe definitely planned ahead and contacted the hotel weeks in advance to discuss certain things he wanted to do."
"He didn't want to propose in a public setting, even though there are so many beautiful spots on the hotel grounds that have spectacular views and are well-known as places where people pop the question," the source adds.
Eventually, it seems Manganiello, 38, opted to propose to the Modern Family, 42, star in their palatial suite.
"It has unobstructed views over the water and almost seems like you are floating on the ocean," said the source, who believes the proposal happened at sunset and included champagne followed by several sweet treats. "Desserts were sent later on."
After the happy event, the source tells PEOPLE, the newly betrothed couple "weren't seen around the hotel much on Christmas Day, which many took to mean they were busy ... celebrating."
The couple eventually emerged to lounge by the pool, where a photographer captured Vergara wearing a stunning diamond ring.
The island fairy tale wrapped up for the couple on Monday, when they were photographed walking hand-in-hand through Los Angeles International Airport.
This will be the first marriage for Manganiello and second for Vergara, who has a 22-year-old son, Manolo. He first met the Colombian-born beauty briefly at the MTV Movie Awards in 2012.
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