The Batman Begins star and Jamie, who has been linked to the actress for some time, arrived at the Las Ventanas al Paraiso resort in Cabo San Lucas on Friday, two days before celebrating her special day on Sunday.
"Katie and Jamie took a private jet to Cabo on Friday morning from Van Nuys Airport (in Los Angeles)," a source tells Us Weekly magazine. "It was a quick trip in honour of Katie's birthday. It was only them and two pilots on the plane."
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"They stayed in one of the most private suites at the hotel, separate from other guests and entered by a small path," the insider continues. "They wanted to be very discreet and had everything delivered to their room and taken care of by a personal butler."
The romantic getaway was a quick one - the pair returned home to Los Angeles on Saturday.
Katie and Jamie first sparked gossip of a secret romance in 2013, but the stars, who are known for their guarding their privacy, have never publicly commented on the relationship rumours.
However, they've been spotted out together on many occasions and it was previously thought the actress would unveil the romance soon.
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"She's ready to go public and show the world how in love they are," an insider told Britain's Closer magazine earlier this year. "She wants him by her side at red carpet events."
Katie triggered engagement rumours back in January, 2016 when she showed off a ring on her left wedding finger, although Jamie's representative dismissed claims of an impending wedding.
Katie was married to Tom Cruise, the father of her young daughter Suri, from 2006 to 2012 and Jamie has daughters Corinne Bishop and Annalise from previous relationships.
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