6:24 AM PT -- 8/9 -- Turns out the third person walking with the happy couple WAS Matt. It should be no surprise, the actor has been a major public supporter of Ben's renewed relationship -- and the two have been friends for decades.
Jennifer Lopez and Ben Affleck aren't shying away from their love here in La La Land -- as if their big date night on Saturday wasn't enough ... here's more evidence from the day after.
Check out these photos TMZ obtained of Bennifer holding hands for a romantic stroll on the beach late Sunday afternoon ... one that's kinda tucked away in Malibu near Paradise Cove, below what we're told seemed to be a private home (perhaps one of theirs, or a pal's even).
Unclear who exactly the guy third-wheeling with them was, but eyewitnesses tell us he seemed to be part of their crew as they took a walk to remember. We *think* that looks like someone we recognize -- and who Ben certainly recognizes too. That you, Matt Damon???
Still ... it's a pretty romantic outing, even away from the public eye so to speak -- which speaks volumes about where they are right now (aka, head over heels in love). Remember, they'd just hit the town the night prior in a big "we're here" type of way.
Before the big Bev Hills debut, they'd only been seen getting publicly affectionate on their Euro vacay -- but after this, something tells us we're gonna see a lot more Ben/Jen PDA.