Amal Alamuddin and George Clooney celebrate Rande Gerber's birthday on April 27 in Santa Barbara, Calif.
05/02/2014 at 06:00 PM EDT
was in weekend wedding mode – but not yet his own. Still, his new fiancée
joined him for the fun.
The actor, 52, took a private jet to Cabo San Lucas, Mexico, with his bride-to-be, Amal Alamuddin
, on Thursday.
Sources tell PEOPLE the trip was to celebrate the wedding of Clooney's longtime pal, actor Thom Mathews.
It's not the first trip to the celebrity hot spot for the globe-trotting couple
, who also visited the area during the holidays last year, along with close friends Rande Gerber and Cindy Crawford
This time around, we know just how Alamuddin accessorized her beachwear: with a certain dazzling sparkler.For much more on Clooney's engagement news, pick up this week's issue of PEOPLE, on newsstands now.