Klum is in the midst of a divorce from singer Seal, her husband of nearly seven years and father of four of her children.
She confirmed her new romance on Katie Couric's talk show "Katie" Wednesday.
UsMagazine.com quoted Klum as saying on the program getting closer to Kirsten "just started."
Asked if she would categorize it as a "proper relationship," Klum replied: "I don't even know if I can call it that. I don't know."
Klum said Kirsten has worked for her family for the last four years.
"He's cared for our entire family, mostly for our four children, helped us tremendously," Klum said.
"I trust him with my children's life," she said. "He's a great man ... and we just got to know each other from a completely different side."
Klum's remarks came shortly after Seal accused her in an interview of "fornicating with the help."