Having retired from professional rugby in 2011, Matthew has maintained a passion for sport and is currently studying for his level 3 coaching qualification.
"Obviously it's very disappointing news for me and my family but I'm keen to progress with my treatment and battle the illness with the same commitment as I gave to my rugby career," he said.
"I would like to thank everyone who has offered their support and the fantastic support from the guy's at Velindre Cardiff. I am determined to continue my everyday life with my family and friends and appreciate the privacy shown during this very difficult time."
Welsh Rugby Union Group Chief Executive, Roger Lewis, said: "All our thoughts are with Matthew and his family at this extremely difficult time.
"In winning 19 caps for Wales, Matthew proved that he had the talent to excel at the highest level and always displayed true Welsh flair in his play.
"Throughout his career he was always a favourite with the supporters who recognised his talent and enjoyed his incisive contributions to all the games he took part in.
"Matthew embraced the professional era and retained a determination to contribute at the elite level where his skills could be displayed at their best.
"He is a young man who can be extremely proud of his rugby achievements and the friendships he forged both on and off the field of play.
"Those friends and the rugby followers who enjoyed watching him play will be greatly saddened to learn of his illness and Matthew can be assured we are as one in thinking of him now."
(Matthew J Watkins has requested that media respect his privacy and that of his family by accepting the above comments and making no further attempts to make contact at this time)