The couple took a private jet to Mexico last Thursday and celebrated the actor’s 53rd birthday on Tuesday.
According to sources, the pair will watch George's close friend Thom Mathews tie the knot with Kara Jensen on May 10.
It's not the first time George and human rights lawyer Amal have been to Cabo together. They visited George's holiday home in El Salvador last year with his friends Rande Gerber and Cindy Crawford.
This year, however, Amal has a new accessory in her holiday wardrobe – the stunning emerald cut diamond ring presented to her by her husband-to-be, which is reportedly worth $750,000.
The couple toasted their engagement at a birthday dinner for Rande earlier this week in Santa Barbara, California.
"George and Amal are trying to keep things very low-key but they also aren't really trying to hide this," a source tells Hello!.
"I think it's like they want people they love to know that this is for real, that they plan on being together forever."