More than a decade on from their split, there's clearly still bad blood between Sophia Bush and her ex-husband Chad Michael Murray, who she's publicly labelled a "f***boy."

The pair met as co-stars on hit show One Tree Hill - tying the knot in 2005 before separating just five months later.

The cause of their breakup was brought up by an Instagram user in a personal attack on the 34-year-old actress during a heated political debate this week.

Bush and Murray with the cast of One Tree Hill.
Bush and Murray with the cast of One Tree Hill.

After Bush declared her support for Hillary Clinton, a user tweeted at her "So @sophiabush you side with liars? No wonder Chad cheated on you, your taste sucks. UNFOLLOW."

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The Chicago PD star - who recently hit out on Twitter at a "creepy" fan who harassed her on a plane - wasn't going to let the inappropriate comment slide.

She replied: "Super classy, Ally. Yes I side with the most experienced person to ever run over a white supremacist, pathological liar who is a crook that has defrauded our government. And claims that doing so makes him "smart." Much like him you seem to blame women for their f**kboy partners' actions. Hope that kind of karma doesn't sucker punch you some day. Good luck in life to you. You seem to need it."

Sophia Bush posts comments about ex Chad Michael Murray. Photo / Instagram
Sophia Bush posts comments about ex Chad Michael Murray. Photo / Instagram

Bush was quickly inundated with messages of support from fans, praising her for sticking up for herself and being "a great role model."

The incident clearly dredged up distressing memories for the actress, who originally attempted to have the marriage annulled on the basis of 'fraud' back in early 2006.

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It was denied, and the pair had to settle for a divorce later that year.

Despite the messy breakup, Bush and Murray continued working together in close quarters on One Tree Hill until the series wrapped in 2009.