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A security guard filed a lawsuit against Kris Jenner and Kourtney Kardashian, claiming they sexually harassed him with sexual comments and overtures ... but Kris and Kourtney call it "fabricated and false fiction" by a disgruntled ex-employee.

Marc McWilliams claims he was hired in 2017 as a security guard to watch over Kris and the fam. He claims in May 2017, he became subject to "a pattern of unwanted and unwelcome sexual advances and other harassing misconduct" from Kris. Among his claims ... comments of "an overt sexual nature," comments about his physical appearance, comments about his sexual activities, and comments that he engage in a sexual relationship, among other things.

McWilliams claims, among other things, Kris massaged his neck, shoulders, arms and back without his consent, caused her hand to rest on his thigh and groin, caused her pelvis to rub against his back and/or rear end, and claims she exposed portions of her body to him. He also claims she made "lewd suggestive, sexual, sexist, racist, homophobic and otherwise discriminatory comments at him and his co-workers."

He claims Jenner then engaged in a pattern of conduct "involving non-consensual physical contact" with him. He says he complained to the H.R. dept. of his security company but the complaints were ignored.

Kris' lawyer, Marty Singer, tells TMZ, "Kris categorically denies ever behaving inappropriately toward Marc McWilliams. The security guard worked outside the house and he never even went into Kris' house."

Singer goes on ... "Kris had very little interaction with him. After the guard was repeatedly caught sleeping in his car while on the job, the security company was asked not to assign him to work there in the future."

As for why he's suing Kourtney as well ... he claims she was also responsible for what he claims is retaliation.

Singer goes on to say ... "The guard never made any complaints to his employer about Kris until contriving this ludicrous claim." He adds, "Although Kourtney is named in the suit, she is not accused of doing anything improper with the guard, nor did she do so."

There's also this ... McWilliams was a founding member and a close friend of R. Kelly. The two founded the music group MGM in the late '80s and McWilliams was also listed as a part of the "Surviving R. Kelly" series.

As for Singer, he ends by saying ... "It is outrageous that anyone can sue anyone in America and believe there is no recourse when pursuing fictional and meritless claims. When Kris and Kourtney defeat this ridiculous, frivolous lawsuit they intend to immediately sue McWilliams and his attorneys for malicious prosecution."