Monica Lewinsky is promising to reveal secret love letters to Bill Clinton and his penchant for kinky sex in a new tell-all about her days as his favorite intern.

Lewinsky, who turns 40 next year, is out for “revenge” and ready to air bombshell details from her Oval Office trysts with the former Horndog-in-Chief in a $12 million memoir, according to friends.

Lewinsky never got explicit in past interviews about her Clinton encounters, but now plans to describe his “insatiable desire for three-way sex, orgies and the use of sex toys of all kinds,” one pal told the National Enquirer.

The purported details of the potentially embarrassing tome come after the Post’s Page Six reported last week that Lewinsky was shopping a tell-all to several publishers.

According to her friends, Lewinsky also will recount how Clinton referred to wife Hillary as a “cold fish” and “laughed” about their “non-existent sex life.”

She’ll also release love letters she wrote to Clinton.

“In them, she opened her heart about her love for Bill and how much happier she could make him,” said the source. “Some of what she wrote was so raw that she never sent them.”

Lewinsky could not be reached and her reps didn’t return calls.

In the 14 years since she became a national punch line, Lewinsky has gotten her master’s degree, worked briefly as a news correspondent and launched a failed handbag line.

“No one will hire her and she can’t get a job because of Clinton,” a sympathetic friend told The Post yesterday. “She needs to make money somehow.”