Jennifer Aniston and Justin Theroux enjoy a Mexican vacation with famous friends

Us Weekly

Couples only!

Jennifer Aniston and her fiancé, Justin Theroux, turned their intimate Mexican getaway for two into a fiesta for six when they invited pals John Krasinski, Emily Blunt, Jimmy Kimmel and Molly McNearney to join them in Cabo San Lucas after Christmas.

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A source tells Us Weekly that the two married couples boarded a flight at Los Angeles International Airport on Thursday, Dec. 27, for a little post-holiday trip together.

"The whole group walked out of the Admirals Club lounge and over to the terminal," the onlooker says of the friendly foursome. "John's arm was around Emily, and they were smiling -- very couple-y and cute. [They're] clearly very happy."

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Adds the source, "The group looked very excited to be vacationing together."

As they should be! Upon arriving in Mexico, the stars joined A-list lovebirds Aniston and Theroux, who have been soaking up the south-of-the-border sun since before Christmas.

"They spent the afternoon lounging around and having drinks [at Jen and Justin's house]," an eyewitness tells Us, noting that the hosts had someone catering to their guests' every whim. "They seemed to all be really good friends and comfortable around each other. Emily was lying in John's lap, and Jen had her arms around Justin. They were there all afternoon until sunset, laughing and having great conversation."

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Indeed, Theroux and Aniston's home seems happier than ever these days. After meeting on the set of "Tropic Thunder" in 2007, the two reconnected while filming the movie "Wanderlust." On Aug. 10, the actor's 41st birthday, he proposed to his bride-to-be in New York. They have yet to announce a wedding date.

Click through to see more photos from their vacation...