Kevin Boyle appeared on the star's 2002 U.K. TV show Jamie's Kitchen, which saw Oliver give 15 unemployed youngsters the chance to work at his Fifteen Restaurant in London.
Boyle disappeared in October (11) and his body was discovered in land near his home in south London last week (ends22Jan12), and Oliver has now spoken of his heartbreak after hearing the terrible news.
In a statement, he says, "I'm deeply saddened by this tragic news. I am proud to have been able to call Kevin a friend for 10 years.
"He was also a constant supporter of Fifteen and all the apprentices and graduates who came after him through the course. I last saw him in September 2011 at the graduation ceremony for the ninth group of apprentices and he was on good form, which makes this news even harder to take. My thoughts are with his family at this incredibly difficult time."
A Scotland Yard spokesman adds, "The death is being treated as unexplained at this stage. A post mortem will be arranged in due course."