The chef paid tribute to Ben Watkins, who died at the age of 14 after a battle with cancer.
Ramsay wrote on Instagram: “We lost a Master of the @masterchefjunior kitchen today.
“Ben you were an incredibly talented home cook and even stronger young man.
“Your young life had so many tough turns but you always persevered.
“I adored our time cooking and laughing together on set.
“Heartbroken today losing my little mate, sending all my love to Ben Watkins’ family with this terrible loss.”
Watkins, who lost both his parents in 2017, appeared in the sixth series of the US show when he was 11.
A statement from his grandmother and uncle on a GoFundMe memorial fund page said: “Our Ben went home to be with his mother this afternoon after a year-and-a-half-long battle with Cancer.
“After losing both of his parents in September 2017, we have marvelled at Ben’s strength, courage and love for life. He never, ever complained.
“Ben was and will always be the strongest person we know.
“When Ben’s rare illness was shared with the world, he was so heartened by the outpouring of love he received from every corner of the globe – especially here in his hometown of Gary, Indiana.
“We cannot thank this community enough for holding our family up in prayer and for all that you’ve done.
“Ben suffered more than his share in his fourteen years on this Earth but we take solace in that his suffering is finally over and in that, in the end, Ben knew he was loved by so many.”
The memorial fund has already raised more than 200,000 US dollars (£151,000).