How Heidi Klum's Husband Tom Kaulitz Asked Her Kids 'For My Hand' Before Proposing on Christmas Morning (Exclusive)

Heidi Klum still blushes when she thinks about the touching way her husband Tom Kaulitz involved her children in his proposal.

While reflecting on America's Got Talent contestant Richard Goodall's tribute performance to his fiancée, the NBC judge exclusively told PEOPLE about one of Kaulitz's most loving gestures.

"The sweetest thing that my partner has done for me is that he asked my kids first if he could ask for my hand," she smiled. "So he kind of was in cahoots with my kids."

"They figured out how they were going to do it and then they all surprised me on Christmas morning six years ago. I thought that was so nice that he involved my kids," she added.

Klum, 50, and Kaulitz, 34, began dating in 2018 — a few years after finalizing her divorce from Seal, with whom she shares her four kids: Leni, 20, Henry, 18, Johan, 17, and Lou, 14. The pair quickly fell in love and secretly tied the knot in February 2019.

After watching contestants Rhythm & Roni strut their stuff on stage during an Aug. 13 episode of AGT, the former supermodel revealed that she and Kaulitz had been taking dance lessons to spice up their marriage.

Despite their efforts, Klum confessed to PEOPLE that her husband didn't have a great sense of rhythm and the two were still stuck on their first routine.

"We started with rumba. It's not going very well," she laughed. "I thought because he's a musician, so I thought he has a good feeling for beat and all of that stuff."

According to Klum, the music producer can play "any instrument" and feel the beat in his craft "but when it comes to dancing, I don't know. I'm like how is this possible?"

"I want to do proper stuff with him because we want to grow old together," she explained. "So there's so many places where you have the opportunity to dance and I love dancing together."

While Klum can easily remember a step once she learns it, Kaulitz has "two left feet when it comes to this so we need a lot more practice."

"I thought we would be already past rumba. I thought we already moved on to [the fox trot] for something and we are still on the first same dance," she quipped. "We started in January as a New Years resolution and we're still on the first."

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America's Got Talent airs Tuesdays at 8 p.m. ET on NBC.