Justin Baldoni's 'It Ends with Us' Double Pulls Back Curtain On 'Tense' Set

Justin Baldoni and Blake Lively's issues on the "It Ends with Us" set weren't known to everyone, but they certainly affected the vibe ... so says Baldoni's stand-in.

Thomas Canestraro -- Baldoni's stunt double on the film -- spoke with Daily Mail about his time on set near the end of filming ... admitting it felt "tense" -- and, "There was some discomfort from everybody."

Canestaro says the big problem he noticed were the production issues ... claiming he was meant to be on set for just five days -- but, that quickly turned into two weeks.

TC remembers wondering why each scene seemed to take so long to shoot ... and, with hindsight, he says the delays make far more sense.

Canestraro also claims that Blake's demeanor was far different than he remembered it being when the two met on the set of "A Simple Favor" several years prior.

During a promotional shoot which involved Lively on 'ASF' -- where Thomas stripped down to only a "sock" covering his privates -- says he had an "extremely easy time" working with Lively.

However, on 'IEWU,' Thomas claims she was more "closed off" ... and, while he thought it was cool that Ryan Reynolds was visiting the set at the time, Thomas now admits it might be because of how difficult the shoot was for Blake.

A source close to Blake tells TMZ ... it shouldn't be surprising that she was "closed off" -- given the sexual harassment allegations she later made against Justin.

As for his thoughts on Baldoni ... Canestraro says they didn't stay in contact after shooting -- but, he was "extremely friendly."

As you know ... Blake and Justin are suing each other -- with Blake alleging Justin sexually harassed her and Justin claiming Blake tried to take over "It Ends with Us" from him.

Quite frankly, there are too many developments for us to catch you up on here ... but, check out our video timeline detailing their legal battle.