Cowell also recalled Payne’s first X Factor audition in 2008, at the age of 14, when Cowell told the budding singer he was not ready and to come back in two years.
“A lot of people would have given up. You didn’t. You came back and within months the whole world would know Liam.
“And you never forgot the fans. I watched you spending so much time with people who had wanted to meet you. You really cared.”
Cowell eventually signed One Direction to his label and masterminded their global success before they split in 2016.
The music mogul also revealed that Payne had visited him last year.
“Not for a meeting. Just to sit and talk. And we reminisced about all of the fun times we had together. And how proud you were to be a Dad,” he wrote.
“After you left, I was reminded that you were still the sweet, kind boy I had met all of those years ago.”
He added: “I have met your son, Bear. He has your smile and that twinkle in his eye that you have. And he will be so proud of everything that you have achieved. And how you achieved it.”
Cowell’s tribute came after Payne’s former bandmates posted their own heartfelt memories.
“I always thought the five of you in the band as brothers,” Cowell continued. “And regarding their messages today I believe you were.
“And now Liam, I can see the effect you had on so many people. Because you left us too soon.”