New York- Sharon Bush tried to back away yesterday from quotes Kitty Kelley attributes to her in her new slice-and-dice book on the Bush family – but she may have backed into a smoking gun.

In her book “The Family: The Real Story of the Bush Dynasty,” Kelley claims that the blond beauty told her: “[George W.] Bush did coke at Camp David when his father was President, and not just once, either.”

Sharon, who was married to President Bush’s brother Neil for 24 years and is the mother of model Lauren Bush, released a statement through her lawyer, David Berg:

“I categorically deny that I ever told Kitty Kelley that George W. Bush used cocaine at Camp David – or that I ever saw him use cocaine at Camp David. The one time I met in person with Kitty Kelley, she mentioned drug use at Camp David. I responded by saying something along the lines of, ‘Who would say such a thing?'”

Earlier, White House spokeswoman Claire Buchan told us: “We haven’t seen the book, but based on reports, it’s obvious that it’s filled with garbage that has been discredited, disavowed and dismissed years ago.”

But Sharon has one small problem: There was a third party at the lunch, an unimpeachable source who agreed to speak with us on condition of anonymity, who says Kelley’s quotes are accurate.

“We met at the Chelsea Bistro on April 1, 2003,” says our insider. “It was a very long lunch. Sharon was talking about affairs in the Bush family … [that they are] very dysfunctional. She said they talk about family values, but they don’t practice what they preach.

“Then Kitty raised the drug issue,” our source continues. “Kitty, who can make a rock talk, said: ‘I know about the drugs. I know that W did drugs at Camp David during his father’s presidency.’

“Sharon agreed. She said, ‘Absolutely. That’s all true.'”

Meanwhile, Kelley’s associate publisher Suzanne Herz said: “Doubleday stands fully behind the accuracy of Ms. Kelley’s reporting, and believes that everything she attributes to Sharon Bush in her book is an accurate account of their discussions.”

“The day following this lunch, in the presence of her editor, Peter Gethers, Ms. Kelley had a subsequent telephone conversation with Sharon Bush which lasted approximately 1-1/2 hours. Ms. Kelley has notes to corroborate both of these conversations.”