Matthews, 34, was just 10 when his brother died in 1999 after becoming the youngest Brit to climb Mount Everest.
“I never really processed Mike's death until just now,” he said on his new podcast titled Big Fish.
“He died in 1999, 23 years ago and he was 22, the youngest Brit to reach the summit. And I was 10, so, to me, losing him was not something I fully understood,” he continued.
Matthews said his brother was like a “superhero figure” and he struggled to come to terms with his death.
“I just assumed he'd come back, I didn't believe that he was dead for a period of time,” he said.
“And you know, as time passed, I understood I would never see him again. I've always had this burning desire to find him. And obviously I understood through my teenage years, how complicated that would be.”
Hours after reaching the Everest summit, Michael died after becoming separated from his mountaineering group and his body has never been found.
In August, Matthews announced a new Disney+ documentary, Finding Michael, in which he embarks on the journey to Mount Everest in an attempt to recover his late brothers’ body.
“During recent years the question of whether or not Mike could be found and brought home to our family was on my mind. I became uncomfortable with the thought of him being left up there, possibly in plain sight,” Matthews said in an Instagram post announcing the documentary.
“So, 23 years after his death and with my family's support and an experience team led by [Nirmal Purja MBE], I travelled to Nepal and trekked to Mount Everest to find my brother and bring him home.”
“This has been the most meaningful and humbling experience of my own life and it is hoped the film will deliver my brave brother the decent legacy that he earned when so young,” he concluded.
On the journey he took for the documentary, Matthews said: “I'm not a particularly externally emotional person. I can't really remember the last time I cried. I'm a very black and white character who just deals with issues when I face them.”
Finding Michael will air on Disney+ in early 2023.