In a new revelation about the Sean Penn divorce, MSNBC.com and Star magazine have reported that Robin Wright Penn filed the dissolution papers after catching the Oscar-winning actor and film director cheating on her.

According to the reports, the alleged incident occurred in the week before Christmas, when the Penns were staying at the Squaw Valley resort in Lake Tahoe, California. Star quoted a source as saying: "Sean didn't spend much time with his wife -- he booked her in a separate suite -- and when Robin got fed up with being alone, she went over to his suite [and] found him drunk with two Russian girls."

Wright Penn, 41, filed for divorce on December 21 and cited irreconcilable differences. They are currently seeking joint custody of their two children, 16-year-old Dylan Frances and 14-year-old Hopper Jack.

The couple has been married since 1996.

Penn, 47, was first married to Madonna from 1985 to 1989 and has starred in such critically acclaimed movies as Mystic River and Dead Man Walking. He recently directed the movie Into the Wild, which is nominated for several Screen Actors Guild awards. In May, he will head the jury awarding the competing films at the Cannes Film Festival.

Click here for two couples counselors' answers to common questions about infidelity.