'The Bachelor': Lace Got Punk'd

It sure looked like an obsessed fan interrupted "The Bachelor: The Women Tell All" episode Monday to show Lace a tattoo of her face on his stomach ... but the guy's actually just a joker.

Our 'Bachelor' spies say comedian and "Punk'd" producer Jamie Abrams faked both his emotions and his tattoo.

Abrams -- who went viral in 2013 for the "The Women of LA" YouTube video -- showed up at the taping and surprised Chris Harrison by standing up and professing his undying love for Lace Morris.

As for the look of fear on Lace's face ... we're told it's 100% real. Our source says no one from cast or crew were in on the prank, so she was understandably creeped out.

We reached out to both ABC and Abrams, but no comment.