The One Tree Hill actress files to end her marriage to costar Chad Michael Murray

One Tree Hill actress Sophia Bush has petitioned to annul her five-month marriage to Chad Michael Murray, PEOPLE has learned.

In papers released by the Los Angeles Superior Court, the actress cited fraud as the grounds for annulling the union. There was no explanation of the alleged fraud.

A fraud claim can be “difficult to prove,” Hollywood divorce attorney Sorrell Trope told PEOPLE. If a judge denies Bush’s annulment request, she can seek a divorce from Murray.

Bush, 23, and Murray, 24, who still costar on the WB show where they first met in 2003, separated in September.

“Sophia went into the marriage believing in the sanctity of marriage,” a friend of the actress told PEOPLE in October, “and Chad simply did not share that vision.”

Renee Zellweger also famously annulled her five-month marriage to Kenny Chesney in December on grounds of fraud, though she clarified in a statement that “‘fraud’ is simply legal language and not a reflection of character.”