Was it really just a prank in which David Letterman saddled Oprah Winfrey with his lunch bill that caused a 16-year rift between the two? No, says celebrity biographer Kitty Kelley. The reasons for the animosity go much, much deeper.

It was Letterman's failure to defend Winfrey from an unruly audience member when she was a guest on his show in the '80s and a series of subsequent digs 'The Late Show' host made at Winfrey's expense that cemented their rivalry, Kelley writes in The Huffington Post.