Actress Kaley Cuoco has officially filed for divorce from her husband Ryan Sweeting, citing "irreconcilable differences".

According to documents obtained by people.com. on Monday, the two had a pre-nuptial agreement, which was signed in November 2013, one month before their New Year's Eve wedding. 

The court documents also explained that Cuoco and her husband were separated as of September 3. 

Cuoco, 29, and Sweeting, 28, "mutually decided" to split after 21 months of marriage, her representative said.

"The Big Bang Theory" star gave no signs of marital issues when she gushed about her ex-husband and his relationship with her ex and current co-star Johnny Galecki on "Watch What Happens Live!".

However, the couple had hit the rumour mills of relationship trouble since April. 

"The few times Kaley and Ryan were out together, the tension was noticeable. You could tell the honeymoon phase had ended," said a source.

"They both seemed miserable."