Larry King Affair in Play in Divorce?

Did an affair between Larry King and his wife's sister lead to the end of his longest marriage?

Not to hear her tell it.

King and wife No. 7, Shawn Southwick-King, have both filed for divorce after 13 years, King spokesman Howard Rubenstein confirms, adding that she filed minutes after her husband did.

It's King's eighth divorce - he divorced his second wife twice.

The 76-year-old host of CNN's long-running "Larry King Live" and Southwick-King, 50, have two sons, ages 11 and 9. King is seeking joint custody of the boys. He's also asking a court not to award Southwick-King, 50, any spousal support.

"His major concern is the welfare of his children," Rubenstein says.

Both parties are citing irreconcilable differences as the cause of the breakup.

But rumors have surfaced of a supposed affair between King and his sister-in-law, 45-year-old Shannon Engemann.

Engemann denies the rumors to celebrity Web site TMZ.com, which first reported that King and his wife were calling it quits.

"I'm tired for taking the rap for things," she said to TMZ. "I did not have an affair with Larry. He's been like a father to me."

Just this past February, points out CBS News Correspondent Michelle Gielan, the couple joked about having problems in front of TMZ cameras.

But the jokes are over and both sides are preparing for a fight that will likely include a battle for ownership of a Beverly Hills mansion and two homes in Utah.

King married Southwick-King in a hospital room in 1997 three days before surgery to clear a clogged blood vessel.