Playboy Playmate Karissa Shannon Says Her Son Will Be Nothing Like Hugh Hefner

Hugh Hefner is the last man Karissa Shannon wants her unborn son to take after ... and she's already planning to raise him differently.

The former Playboy Playmate told Page Six she's determined to raise her son, Genesis, to be the complete opposite of Hef ... saying she wants him to be a gentleman with manners who "leads with his heart."

Karissa also revealed she's engaged to a mystery man, whom she describes as a "simple, blue-collar guy" from Canada.

She's keeping her fiancé's identity under wraps ... but says the 44-year-old accepts her past, loves her unconditionally, and has helped her develop healthier drinking habits.

As TMZ previously reported ... Karissa has accused Hefner of trying to pressure her and twin sister Kristina Shannon into sexual activity with each other while they lived at the Playboy Mansion.

Hefner's widow, Crystal Hefner, also recently claimed the Playboy founder allegedly tried to physically force the twins to perform oral sex on each other ... calling the alleged behavior "incest" and "disgusting."

Karissa, who revealed her pregnancy in August, says she's worked hard to leave her Playboy days behind ... trading the mansion lifestyle for a quieter life in Michigan.