"It's my wedding day!!!!" Tweeted the Big Bang Theory actress, before confirming that it was actually part of her character's costume in The Wedding Ringer. "#theweddingringer #fakeweddingcalmdown."
The photo showed Kaley eating a yoghurt and sporting pink flip-flops as she took a quick break from filming the movie which also stars Alan Ritchson and Kevin Hart.
Kaley announced her engagement to her tennis player boyfriend Ryan Sweeting last month after a whirlwind courtship of just three months.
"It's only been three months but she knows Ryan is the one," a source told US Weekly. "When you know, you know."
The 27-year-old has said that she was completely surprised by her handsome beau's proposal as he "actually started a little fight with me and threw me off."
"I was like 'Oh my God, things aren't great.'" added the actress, but the Ryan's decoy went perfectly to plan. "He surprised me at the end of the night ... [when] he popped the ring out. It was amazing," she told Entertainment Tonight, speaking from the set of her new film The Wedding Ringer.