'Big Bang Theory' star Jim Parsons pranks Kaley Cuoco on her birthday

Fans of the Big Bang TheoryBig Bang Theory.

Now it seems it's Cuoco's turn to be disappointed.

The actress -- who plays Penny on the TV series -- turned 33 on Friday. Getting up to some mischief, her co-star Jim Parsons took it upon himself to sabotage the cast and crew's carefully made surprise birthday plans for her.

Parsons, 45, sneakily shared a snap to Instagram of her pink birthday cake in its box, before they gave it to her. Uh-Oh.

"Almost time @kaleycuoco," wrote the 45-year-old actor. "Shhhhh....."

Taking it a step further, Parsons was even so bold as to tag Cuoco in the pic, just to, you know, make sure she saw it.

Fans were quick to draw comparisons to his IRL behaviour with Sheldon who he plays on the show.

"Sheldon doesn't know how to keep a secret!" wrote one.

Another commented, "What Sheldon Cooper would have done as well…"

"Tag her so that she doesn't know. That's smart like Sheldon," added another.

https://www.instagram.com/p/BerKEcdHU3L/

The actor later shared a second pic of a rather unimpressed looking Cuoco.

Looking dead pan at the camera, Cuoco is featured holding up a phone displaying Parson's earlier snap of her birthday cake.

"Oops @kaleycuoco," he wrote.

Oops indeed!

It seems that there's no hard feelings between the two and that she actually may have even seen the funny side judging by her comment on his post that implied she was rolling on the floor with laughter.

"ON THE FLOOR."