Heidi Klum Dishes on Her 'Prank'-Filled Boating Day with 'AGT' Judges That Simon Cowell Abandoned (Exclusive)

The 'America's Got Talent' judge tells PEOPLE all about her "amazing" day on the water with fellow judges Sofía Vergara and Howie Mandel — and why Simon Cowell was not in attendance

Heidi Klum won't pass up the chance to have a good time on the water, especially if it involves her America's Got Talent costars!

Speaking to PEOPLE backstage after night one of AGT's season 18 finale, the supermodel judge, 50, opened up about her recent day boating with fellow judges Howie Mandel and Sofía Vergara — and why Simon Cowell missed out.

Klum revealed that all of the judges made plans to go on Mandel's boat on Monday. "He has this gorgeous boat, and he just wanted to just be nice and invite us on. He had an amazing chef there. We were eating yummy sushi. I think he wanted to show off his boat," she explained of Mandel, 67.

However, Cowell, 63, mysteriously never showed up. Because the judge famously doesn't use a cell phone, they couldn't simply call or text him to ask where he was.

"We all made plans. Who does not show up? Simon," Klum recalled. "We all [were] like, ‘Where the heck is Simon?’ We waited a little bit at the dock and then we left. Maybe he actually did come in the end and we don't know."

Related: Meet the 11 Finalists of 'America's Got Talent' Season 18 (Exclusive)

Before the live AGT show on Tuesday, the model said she confronted Cowell and asked him why he hadn't shown up to their planned boat outing.

"I was like, ‘Where were you?’ And he was like, ‘Oh, was that yesterday?’" she shared. "He fully knows, but he's saying it with a smile on his face."

Cowell wasn't the only one who got involved in some mischief that day. Klum told PEOPLE that she also pulled a little "prank" of her own on Mandel.

"I picked up Sofía, and then when Sofía saw what I was wearing, she was like, ‘I have to change.' Then we went into her closet and it took another 40 minutes," she joked. "And then Howie is like, ‘Where are you?’ And I said, ‘Oh, it was today?’ He's, like, calling me."

"Sometimes I like to do a little prank on him too," she added with a laugh.

Related: Heidi Klum Says She Almost Drew Childbirth Instead of Her Wedding During 'AGT' Magic Act (Exclusive)

It's far from the first time the America's Got Talent judges have joked around with each other. The group has had plenty of banter-filled moments while judging the NBC reality series together over the years,

Earlier this season, Vergara, 51, walked off stage after Mandel cracked a joke about her newly single status, following her divorce from estranged husband, Joe Manganiello.

The quip came when the Modern Family actress was tasked with taking a lie detector test on stage at Cowell's request. When Mandel jokingly asked if there was anyone in the audience she was interested in, she declared that she'd had enough.

"That's it!" Vergara shouted, returning to the judges' table with a laugh.

Related: 'AGT': Blind Singer with Autism Who Was Adopted by Her Teacher Earns Heidi Klum's Golden Buzzer

During Tuesday's episode of AGT, all 11 finalists performed one final time for the judges and America before a champion is crowned on Wednesday. The acts included dance group Murmuration, comedian Ahren Belisle, singer Putri Ariani, singer Lavender Darcangelo, balancing duo Ramadhani Brothers, the 82nd Airborne Division All-American Chorus, magician Anna DeGuzman, dance group Chibi Unity, Adrian Stoica and his dog Hurricane, the Mzansi Youth Choir and dance group Avantgardey.

Speaking about Darcangelo's finale performance, Klum had nothing but great things to say about her Golden Buzzer-winning act.

"She nailed it. She was fantastic. She looked beautiful. She sounded beautiful," Klum raved. "Her boyfriend was there. I kept on peeking over to him and he was sitting there super proud, and I said to him, I'm like, 'Are you nervous?' And he's like, 'I'm not nervous. She's not nervous. She's just excited.' So it was beautiful. It was a beautiful journey for her."

"I'm hoping that America will vote for her," Klum added. "I hope that she will win tomorrow. I also love what everyone said there to her today... It was all around A plus plus."

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The season 18 finale of America's Got Talent airs Wednesday at 9 p.m. ET on NBC.

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