Larry King: Divorcing Shawn Southwick; Cheating with Her Sister Shannon Engemann!

Larry King is divorcing his eighth (!) wife Shawn Southwick amid rumors that the CNN personality had an affair with Shannon Engemann, her own sister.

This has the makings of a nasty Hollywood divorce scandal.

Sources directly connected with Larry King and Shawn Southwick say that his alleged infidelity is the cause of the breakup, and not just any infidelity.

Shawn believes Larry has been having an affair with her sister for five years ... and the cover was blown when Shawn checked his Visa statement!

A source says Larry bought expensive gifts for Shannon Engemann - we're taking real expensive, like a $160,000 car and "tons of gifts from Cartier." 

The credit card bills were paid by Larry's business manager, but when Shawn starting looking at the statements, she saw a Cartier diamond necklace.

Her classic response? "He never gave me a diamond necklace."

Larry King with wife Shawn Southwick, left, and her sister Shannon Engemann.

Engemann denies anything inappropriate took place, although she did admit to receiving the above gifts from King. "This is so ludicrous," she said.

"Shawn has left me threatening messages ... She's singling me out, but Larry has been nothing but generous to our entire family, including me."

Apparently over the past five years, there were numerous instances where the couple was fighting over the alleged relationship, sometimes physically. 

A friend recalls an incident where they were "punching each other." But at least to a degree, they made it work, which may come back to bite King.

Several years ago Larry attempted to save the marriage by transferring three homes into Shawn's name, including the Beverly Hills house they live in.

Shawn is seeking primary custody of their two kids and claiming much of the real estate as her own property, including the Beverly Hills house. Ouch.

Larry, 76, and Shawn, 50, were married back in 1997 and have two sons together. Both cite "irreconcilable differences" in separate divorce filings.

THG TIP FOR THE LADIES: When you're wife #8, don't expect the guy is going to be much good at marriage. And hide your younger siblings.