Cesiah and Alex are like many sblings. Cesiah, 21, says that her 17-year-old brother is her best friend.

“Me and him are super close,” she told Inside Edition. “He’s my best friend.”

Unlike many siblings, though, their bond has been forged through multiple illnesses — and it’s miraculous that Alex has made it this far.

At just 18 months old, he was diagnosed with ataxia telangiectasia, a rare disorder that progresses over time and affects multiple bodily systems. Most people with this condition will use a wheelchair at some point, and most do not live past their teen years.

Unfortunately, according to the U.S. National Library of Medicine, this condition also puts people at risk for other issues since they have a compromised immune system, and they are susceptible to certain deadly forms of cancer.

At 3 years old, Alex was diagnosed with leukemia and doctors said he had a 10% chance of survival.

Despite these setbacks, he was able to beat cancer — no doubt in part because of the love and support he received from his family.

When Cesiah got engaged in 2017, Alex made her an amazing promise. “Since I got engaged, he said, ‘Cesiah, I don’t know how I’m gonna do it, but I’m gonna dance with you,” Cesiah said.

Though he used a wheelchair and had only limited use of his legs, he was adamant that they would dance at her wedding. They planned for him to stay in his wheelchair while they danced, but at the last minute Cesiah switched things up.

“We practiced a little bit, incorporating the wheelchair, but when it came to the wedding day, I forgot everything,” Cesiah admitted. “I blanked out so I was just like, ‘You know what? I’m gonna carry him.’ So I carried him.”

She swept him up and the two hopped around the dance floor. She later said that while they danced, he told her he wanted her to be happy — and she won’t be forgetting their special moment anytime soon.

“I heard everyone screaming and clapping. It meant the world,” Cesiah said. “I think I’m going to remember as much as I remember saying ‘I do.’”