The Shark Tank star and Johnson, who served as the entrepreneur's pro partner on Dancing with the Stars' twentieth season, met on the show and have clearly been together ever since.
Although the pair has only been dating for less than a year, Johnson, 39, toldPeople, "It feels like a lifetime ago."
"It does," Herjavec, 52, noted, "but it's only been eight months!"
Herjavec had played coy about his relationship with Johnson during the DWTS season and still didn't admit the romance when host Tom Bergeron let the cat out of the bag by saying Herjavec didn't win the mirrorball trophy at the time of their elimination but he appeared to win Johnson's heart.
After their stint on the show, which ended during the eighth week of competition, Herjavec and Johnson escaped on a romantic getaway to Palm Springs, CA.
"I'm very grateful," Herjavec said of meeting Johnson on the ABC reality dancing competition. "It's been great."
"We're really happy," Johnson added while holding her boyfriend's hand at the The Brent Shapiro Foundation 10th Anniversary Summer Spectacular on Saturday.
The couple also playfully described their ideal date.
"Definitely Kym cooking at home," Herjavec told People.
"I'm not the best cook," Johnson said, laughing. "But we eat out a lot, so I'm experimenting with making healthy foods. We like to hang out on the couch and watch a movie."
Dancing with the Stars' next edition premieres Monday, September 14 at 8PM ET/PT on ABC. Johnson revealed which celebrity and professional pairings she'll have her eye on.
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"[Bindi Irwin] is my favorite. I'm going to be backing her. Us Aussies stick together," Johnson admitted. "I'm interested in seeing Gary Busey, too."