Heidi Klum Says She's 'Proud' to See Daughter Leni Re-Wear Her Clothes: 'We Can Upcycle' (Exclusive)

Heidi Klum doesn't mind sharing a closet with her daughter.

At Prince William's fourth annual Earthshot Prize Awards on Wednesday, Nov. 6., the supermodel, 51, said she feels "proud" when 20-year-old Leni gives pieces from her iconic wardrobe a new life.

“I get so excited when I see my daughters re-wearing my clothes," Heidi tells PEOPLE at the event in Cape Town, South Africa. "My eldest daughter, she also is a model, and she goes to events and when she wears my clothes I’m not just proud but we can upcycle.”

In 2022, Leni borrowed her mom's silky black strapless dress from the '90s for her prom.

"Prom night in mamas dress 🖤," the teen captioned an Instagram carousel ahead of the event. Heidi, originally wore the frock in 1998 for a Comic Relief live comedy event and commented a heart-eyes emoji on her daughter's post.

"I'm passing clothes down to my kids," Heidi shared on the Earthshot's green carpet.

"... I think it's so important also to keep wearing your things. I think in the past, we'd wear something once and then we'd never wear it again, and it's so wrong to do," she added. "I urge everyone to wear your amazing things that you have in the closet. It's the best shop, your own closet."

The Earthshot Prize is a global challenge based on five Earthshots – ambitious goals for 2030 to fix our biggest environmental problems. At the awards ceremony each year, five winners are awarded $1.2 million for their contributions in environmentalism. On the carpet, Heidi wore a one-shoulder vintage Halston dress in bright orange.

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“I go to a lot of events but this is probably one of the most important events I’ve been to," Heidi said of the evening. "It is amazing what [Prince William] has done. I have not met him yet. I didn’t know I was on his radar and so when his team called and asked if I could come I said immediately yes."

The America's Got Talent judge says that after she "delved in deeper" to environmental issues, she "learned so many new things."

"Who knew there was sustainable fishing?" she says. "Tomorrow, I’m so honored to go with [Prince William] to this place to learn about sustainable fishing. I knew our waters are overfished and they’re polluted and all of these horrible things. But I didn’t know about sustainable fishing. I love that I get to learn more things and hopefully be better in the future.“

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Her children are what make the future so important to her, Heidi explains. "I have four kids and hopefully I will be a grandmother one day and what about my grandkids? We have to think about our tomorrow," she says.

She adds, “When I was a kid you knew already it was starting and for people to say there is no climate change. I mean open your eyes around you — it’s happening everywhere. There are so many places that I’ve visited where they’re complaining about these things and flooding and everything going on. Everyone needs to open their eyes and being here my eyes are even more open.”