Jay McGraw (search), 26, got engaged to Dahm in Dallas, Chandler Hayes, a spokesman for Dr. Phil McGraw, said Monday.
Dahm exclaimed, "Oh gosh, is this real?" after the Aug. 26 proposal, Hayes said.
The couple will wed in Los Angeles but the date was not revealed.
Jay McGraw designed the 5-carat diamond, emerald and platinum engagement ring.
He told syndicated TV show "The Insider": "I asked her father for her hand in marriage first. I finally told my parents and they are ecstatic. She's the one I want to spend the rest of my life with."
Dahm, 27, and her two sisters appeared in the December 1998 Playboy.
McGraw is a best-selling author of self-help books himself. They include "Closing the Gap" and "The Ultimate Weight Solution for Teens."