The 2011 Playmate of the Year on Monday sought a restraining order against the 21-year-old son of Playboy founder Hugh Hefner, after the son was arrested on suspicion of domestic violence, the Pasadena Star-News reported.

Marston Hefner was released from jail Monday after posting $20,000 bail, according to police and jail records.

Officers were called Sunday night to the apartment Marston Hefner shares with his girlfriend, and he was arrested after she was found with minor injuries, Pasadena police said in a statement.

The woman wasn't identified in the police statement, but Lt. Jari Faulkner told the Star-News (http://bit.ly/z4dVpp) that Claire Sinclair, 20, sought an emergency restraining order against Marston Hefner from police on Monday. Sinclair is the 2011 Playmate of the Year.

It was unclear if the temporary restraining order was granted, and police reached by phone late Monday would give no information beyond the details of Marston Hefner's arrest.

Marston Hefner is one of two adult sons of the Playboy founder and his former wife, ex-Playmate Kimberly Conrad Hefner.

It was unclear if Marston Hefner had hired an attorney. He could not be reached for comment, and the arrest was not addressed on the Twitter accounts of Hugh, Marston or brother Cooper Hefner.

On her Twitter account, Sinclair wrote: "There's two types of pain in the world _ pain that hurts you, and pain that makes you stronger. All of your positivity is giving me strength."

According to her official website, Sinclair was born Clairissa Irene Riccio in Los Angeles and worked as a model as a teenager before becoming Playmate of the Month in October 2011, and later Playmate of the Year.