‘Big Bang' star Jim Parsons blows Kaley Cuoco's birthday 'surprise' with prank Instagram post

Spoiler alert!

"Big Bang" actor Jim Parsons was so excited for his co-star Kaley Cuoco's birthday that he ruined her birthday surprise.

On Thursday, a day before Cuoco's 33rd birthday, Parsons shared a photo of a pink, sprinkled birthday cake which read, "Happy Birthday Kaley" on his Instagram. The star captioned the birthday photo, "almost time....shhh..." and tagged his co-star in the photo.

And while the 45-year-old actor may play a genius on TV, it seems that Parsons didn't totally think the social media spoiler through. Naturally, the Instagram tag tipped off the birthday girl and she discovered the birthday cake photo.

Shortly after posting the "surprise" pic on his account, Parsons posted another photo of a sweatshirt-clad Cuoco displaying the Happy Birthday birthday post on her phone with a disappointed look on her face.

The star known for the character of Sheldon Cooper on the popular CBS series tagged his co-star in the new photo and wrote, "Oops."

But despite ruining the so-called birthday surprise, fans appeared to enjoy Parsons' birthday prank.

One user commented on the photo of Cuoco and wrote, "SHELDON!!! Haha!!!"

Others wrote that the birthday spoiler was "hilarious" and "truly" something that "Sheldon would do."

Like her co-star, Cuoco is also no stranger to sharing cast photos on Instagram.

Recently the actress made fans emotional about the show's last season after she shared a behind-the-scenes photo on Instagram, featuring a selfie of the cast.

“Don’t miss an all new @bigbangtheory_cbs coming at ya TONIGHT!” Cuoco wrote. “A little BTS before curtain call.”

At the end of the caption, Cuoco added the tag "#thefinalseason," referring to the conclusion of the longtime series.

Though the sentimental photo captured a happy cast, fans found the image to be depressing as it further materialized the fact that the series is coming to an end.

“Can’t belive (sic) the show is over,” one fan commented with a crying face emoji.

“The show is not ready to end,” another dedicated fan wrote in the comments section. “There is so much to write about. You guys should strongly recommend not ending this season.”

One user called out Cuoco's image caption and said, “That hash tag is depressing,” while another user begged the cast not to leave and said, “DON’T GO !!!!!!!!!!!!!!!!!!!!!!!!!!”

But while the famous cast is still on the air, they are bringing in the big bucks.

All four of the show's male stars – Galecki, Jim Parsons, Simon Helberg and Kunal Nayyar – topped the list of the Forbes highest-paid actors on TV.

Parsons landed the No. 1 spot making a total of $26.5 million, with Galecki falling behind in the No. 2 spot earning $25 million. Helberg and Nayyar were tied at No. 3 both making $23.5 million.

And like her male co-stars, Cuoco appeared on the highest-paid TV actresses list in the No. 2 spot, making $24.5 million.