Merry in Miami! Katie Holmes and Jamie Foxx Spend Day at Sea on Luxurious Yacht

Katie Holmes and Jamie Foxx kicked off the last weekend of 2018 in style

Katie Holmes and Jamie Foxx kicked off the last weekend of 2018 in style.

The couple, who have mostly kept their four-and-half-year romance away from the public eye, were spotted aboard a private yacht in Miami on Friday.

They both kept it casual for the trip: Holmes, 40, wore a pink pinstripe crop top with matching shorts, while Foxx, 51, sported a black t-shirt and jeans.

Prior to their evening out, the pair spent the day lounging on the luxurious boat, with Holmes rocking a black bikini and Foxx keeping it chill in a white t-shirt.

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The couple’s Florida fun comes weeks after they were seen in New York City together. Holmes and Foxx were joined by Holmes’ mother, Kathleen A. Stothers-Holmes, to celebrate Holmes’ 40th birthday on Dec. 18. The group stopped by popular dessert destination Serendipity 3, where they enjoyed a strawberry sundae and frozen hot chocolates.

“Katie was all smiles,” a source told PEOPLE. “She and Jamie were flirty.”

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The actors were first seen dancing together in 2013 in the Hamptons, a year after Holmes and ex-husband Tom Cruise, 56, called it quits.

Though both have had busy schedules in the last few months, they’ve made efforts to see each other regularly. In November, the two spent time together in New Orleans, where she was filming The Secret and he was working on an untitled sci-fi thriller for Netflix. Foxx visited Holmes on her set and they also enjoyed a romantic dinner date at the trendy Restaurant R’evolution in the city’s French Quarter.

“Their relationship seems so much more serious this year,” a source told PEOPLE in this week’s issue, on newsstands now. “Katie and Jamie keep having public dates, and although they try to not be photographed together, they are clearly not as concerned about keeping their relationship private.”

In September, Holmes made frequent trips to visit Foxx while he filmed his upcoming movie Just Mercy in Georgia, where they enjoyed a bike ride and a gym session together.

“Katie always acts super-excited and giddy when Jamie is around,” said an insider. “They are very cute together.”

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A source told PEOPLE in May the two “are still careful about being photographed together.”

“Everyone knows they are dating, but they still want to keep it private,” the insider said. “After the beach pictures, they only spent time together at home and got extra careful. But this year, they have been more social together. They often go to restaurants for dinner dates, or to hang out with friends.”