Until now, seeing Jamie Foxx and Katie Holmes out together as a couple was as common as a Bigfoot sighting or riding a unicorn ... but not anymore!!!

It took 4 years, but Hollywood's most top secret couple finally packed on the PDA Monday in Malibu ... hand in hand in the sand. Though they've allegedly been together since 2013 -- about a year after her split from Tom Cruise -- this is the first time they've been seen doing what lovebirds do.

As we reported ... Katie was seen with a ring on her finger in March 2016, but Foxx's rep said it wasn't from him. A year before that, Jamie denied they were even a thing. Still, the relationship was no secret to most in Hollywood -- JamKat just never let on in public.

JamKat? Can we slap a ™ on that ... just in case? 

MAKIN' A SPLASH
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