Scandal-plagued talk-show host David Letterman has been rocked by a shocking new bombshell - reports of a sex tape showing him with a female staff member.

A studio surveillance tape reportedly caught the 62-year-old star and a much-younger female co-worker in a compromising position - and it could shatter Letterman's already troubled marriage, say sources.

What's more, the tape could persuade worried CBS execs to hammer the final nail into the talk-show host's late-night career - and could play a key role in the trial of the producer who allegedly tried to blackmail him.

"If the tape makes its way into the criminal case, it'll explode his marriage to smithereens," revealed a close source.

"It's one thing for him to have publicly admitted to having had sexual relations with some women on his staff. It's another to see him in the throes of passion with one of those women.

"Dave apparently didn't know the location of the security cameras at his Late Show studio."

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