Michael Matthews disappeared on Mount Everest in 1999, when his younger brother Spencer was just 10 years old.
Now, 23 years after his big brother's tragic death, Spencer has embarked on the mission of a lifetime, a quest to retrieve Michael's body from Mount Everest.
Michael's body was never found, but it is believed that he is one of the 310 people who died attempting to climb to the summit.
He was just 22 years old when he climbed the mountain and became the youngest Briton to reach the top - before he vanished three hours later.
After finding it 'unbearable' knowing that his brother's body was still on the mountain, Spencer decided to create a documentary of his near-impossible search.
The former Made In Chelsea star revealed that he was haunted by images in his head of his brother dying alone on Mount Everest, with nobody around to help save him.
Appearing on The One Show ahead of the release of his much-talked-about documentary, Spencer admitted that he has never been able to get the stark image of his brother on Mount Everest out of his mind.
And when someone sent his family an image of a body which looked a lot like Michael's, he took it into his own hands to attempt to find his brother and bring his body home after 23 years.
"To be honest, I have always found the idea unbearable of him being out there on the mountain, alone, with people walking past him en route to the summit," Spencer explained.
"Knowing that he was up there, and died alone, has never left my mind. That image has stuck with me."
In a trailer for the documentary, Spencer is seen looking at a picture of his brother, who was wearing a red ski jacket at the time.
Spencer's family were sent a photo of a body, and he believes that it's his brother's.
The former Made In Chelsea star said that he 'hates' the picture because it reminds him of how close to death Michael was.
Spencer filmed the documentary with the help of Bear Grylls and record-breaking mountaineer Nirmal 'Nims' Purja.
In the trailer, Bear warned Spencer ahead of his trip to be careful, reminding him that around seven people die on Everest every year.
He told Spencer that "no mountain is worth dying a second time over".
Spencer recently told Holly Rubenstein's The Travel Diaries podcast: "I was aching to find out more about his death. I was 10 at the time. I remember thinking it was really unfair.
"I always believed that I'd see him again and never took it on the chin that he was dead. I thought it was impossible. It never crushed me in the way it affected my parents and my brother.
"We would read that you could recover bodies from Everest. I know now that you can fly helicopters into Camp 2. For people who don't know Everest, that's quite a big deal," he explained.
Finding Michael launches on Disney+ on Friday, 3rd March.
