A tearful Gray said: ‘He was my best friend for 35 years. He was the pied piper of life and brought joy to everyone he knew. He was creative, generous, funny, loving and talented. I will miss him enormously.’
Mr Lane added that Patrick Duffy, who played his brother Bobby, was also at Hagman's bedside at Medical City Dallas Hospital.
'They had been friends for 35 years and they had worked together for many years, so obviously it is devastating,' Mr Lane told The Sun.
Hagman announced in October 2011 that he had a 'treatable' form of throat cancer and would receive treatment while filming the Dallas reboot.
At the time the star said: 'As J.R. I could get away with anything - bribery, blackmail and adultery. But I got caught by cancer. I do want everyone to know that it is a very common and treatable form of cancer.
'I will be receiving treatment while working on the new Dallas series. I could not think of a better place to be than working on a show I love, with people I love.'
The late actor added: 'Besides, as we all know, you can't keep J.R. down!'