Marston Hefner, son of Hugh, arrested for assaulting Playmate girlfriend (VIDEO)

Marston Hefner, Hugh Hefner's 21-year-old son, has reportedly been arrested on suspicion of domestic violence and charged with battery on a spouse.

Meantime, Playmate Claire Sinclair had obtained an emergency restraining order against Marston Hefner, according to gossip website TMZ, after he "beat her up" Sunday night during a heated argument.

The LA Times reported that Hefner was arrested Sunday evening at a Pasadena home on the 100 block of West Del Mar Boulevard.

The Times quoted Lt. Rick Aversano of the Pasadena Police Department as saying that officers called to the home determined Hefner's girlfriend Sinclair had suffered minor injuries consistent with an assault.

According to E! Online, Hefner was charged with battery on a spouse and released a few hours later after posting a $20,000 bail. (Hefner and Sinclair were not married but under state law a "spouse" can be considered a cohabitant.)

Hefner is one of two adult sons of the Playboy founder and his former wife, ex-Playmate Kimberly Conrad Hefner, according to the Associated Press reported. 

The TMZ website carried a video in which Sinclair says she has obtained a five-day restraining order on Hefner, to give her time to move her things out of Hefner's house.

She said she had called Hugh Hefner after the incident, and that he had expressed sympathy, claiming he was very disappointed by the situation.

According to E! Online, shortly before the alleged assault Sinclair had retweeted a photo of her attending a Grammy-themed fundraiser at the Playboy Mansion with Hugh Hefner and several other Playmates.

Later, she took to Twitter to thank her supporters, writing:

"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."

The AP reported that the alleged assault was not addressed on the Twitter accounts of either Hugh or Marston Hefner, or Marston's brother Cooper Hefner.