Olympic legend Sir Chris Hoy is being treated for cancer. GETTY IMAGES

Six-time Olympic cycling champion Chris Hoy revealed on Friday that he has been diagnosed with cancer, but insisted he is "optimistic and positive" about the future.

The 47-year-old former track racer said he is currently undergoing treatment, including chemotherapy, adding that it is "going really well" and that he feels "fine" at the moment. Writing on his Instagram account, Hoy said: "Last year I was diagnosed with cancer, which was a big shock as I had no symptoms until then."

"I am undergoing treatment, including chemotherapy, which is fortunately going very well. I'd like to extend my sincere thanks to all the medical professionals for their amazing help and care." The Scot added that he had wanted to keep his condition private, but explained that his "hand has been forced" as he looks forward to an "exciting year of work ahead," including the Paris Olympics.

"I am optimistic, positive and surrounded by love, for which I'm truly grateful. As you can imagine, the last few months have been incredibly difficult. However, I feel fine now - I continue to work, ride my bike and live my life as normal," he added.

Born in Edinburgh, Hoy took up track cycling as a teenager and won his first Olympic medal, a silver in the team sprint at the 2000 Sydney Olympic Games. Four years later, he became an Olympic champion by winning the one-kilometre time trial in Athens.

He added to his Olympic medal haul with three more golds at Beijing 2008 and two more at London 2012. Hoy also won 11 world titles before retiring from competitive cycling in 2013.