The proposal, which took place privately in the couple’s suite in the luxurious five-star St. Regis Hotel in Princeville, Hawaii, was carefully thought out.
"Joe definitely planned ahead and contacted the hotel weeks in advance to discuss certain things he wanted to do," said the source.
"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," they added.
Joe, 38, opted instead for their palatial suite, complete with "unobstructed views over the water".
The happy news of the handsome couple’s Christmas engagement broke on Tuesday. A source told E! News: "I've never seen two people so truly in love. The way they talk to each other, touch each other. It's incredible."
The pair, who have been dating for six months, first met in May at the White House Correspondents Dinner, but at the time Sofia was still engaged to former fiancé Nick Loeb – from whom she split later that month.
Sofia's former fiancé Nick was quick to congratulate the Colombian-born beauty. Speaking to Us Weekly, the 39-year-old businessman said: "She is beautiful and majestic and therefore to be loved.
"Beyond all else in life she deserves happiness, the kind that only true love can bring."