Johnny Bananas

Shortly after Johnny Bananas' dear friend and fellow "Challenge" competitor Diem Brown passed away last November, the five-time champ wanted to honor the legacy of the woman he described as a "unique and special soul."

Johnny Bananas

"It was just a simple act of creating a T-shirt and selling a T-shirt and putting a T-shirt in a bag and sending it to people," the athlete tells MTV News about his Diem Strong merchandise, with the proceeds going to D's fundraiser website MedGift. "Now, when it's all said and done, it has the ability to affect the outcome of someone's life. There was never a person -- there was never a face -- that this money was going to help."

But everything changed when JB learned about Kasey Harvey, a 13-year-old Californian battling a rare type of cancer called rhabdomyosarcoma.

"I was trying to reconcile with myself the best way going about doing this and, like divine intervention, Kasey came into my life. All of a sudden, this picture just popped up on my Twitter feed," the "Real World: Key West" alum says of K's tweet, which can be seen below.

"Just the picture alone -- before I even saw the caption -- was just like, 'Oh my god, this is incredible," he continues. "This young girl is wearing my shirt and just with the biggest smile and the happiest look on her face, with the sassiest pose with her hand on her hip. I was like, 'This is it. Done.' She made the decision for me."

With that, J set out to surprise K with a generous gift and an unforgettable afternoon of fitness training. And, as you can see in the video below, the duo instantly bonded.

"She said it was the greatest day of her life, and it was honestly one of the best days of my life -- hands down," JB says.

How did their interaction compare with his "Challenge" adventures, which span nearly a decade?

"All the shows that I've done -- I've been dangled off buildings, I've been stuck on volcanoes, all the crazy s**t MTV has had us do -- I was more nervous showing up at this 13-year-old girl's front door," he dishes with a laugh.

But what makes Kasey even more extraordinary to Johnny are the similarities he sees in the teen and Diem, who he first met on "The Duel" back in 2006.

Johnny Bananas

"It's like Diem 2.0," he states of the young fighter. "It's kind of like I'm getting another shot at trying to help out and lend a hand. Kasey's willingness to show herself to the world, exactly how she is, and allow the world to be there front and center -- that's impressive for anyone. And D was the same way."

+ Be sure to share your words of encouragement for Kasey in the comments -- and follow her on Twitter and Instagram.