A close friend of David Bowie has opened up about the music legend's secret 18-month battle with cancer. Theatre producer Robert Fox shared a close friendship with Bowie for over 40 years. He was among the few close friends and family who knew about his cancer diagnosis.

Bowie died on 10 January, following a secret 18-month battle with cancer. He was 69. The tragic news of his death was announced by son Duncan Jones on social media.

Fox told The Telegraph he found out about the singer's illness in November 2014, when he flew to New York to meet with the production team on the musical Lazarus, which Fox produced and Bowie co-wrote with playwright Enda Walsh.

The singer revealed to Fox, Enda Walsh and director Ivo van Hove that he was battling cancer, believing that it was important they knew. "It was shocking," Fox told The Telegraph. "Nobody knew.. Nobody even suggested there was anything."

Fox said it was characteristic of Bowie, the "private man" to have the "the minimum of fuss". "I think he wanted to protect his family from the insanity there would have been. It would have impinged on the album, Lazarus, his family. And he did it perfectly."

The singer was last photographed in public at the world premiere of the musical on December 12, where he stopped to greet fans and sign autographs. Directed by Belgian theatre director Ivo van Hove, Lazarus is inspired by Walter Tevis's book The Man Who Fell to Earth. Following Bowie's death, unprecedented demand for tickets prompted the company to put on an extra three additional performances in January.

Fox and Bowie first met in London in 1974. Describing the young star who have came to know personally, he told The Telegraph: "He was easy to chat to. He wasn't ostentatious or loud or attention seeking; he was quite shy, modest; very well read and interested in everything, and he liked the theatre."

The producer told The Times the last time he saw Bowie he was 'optimistic', despite his illness and was determined to fight the disease. "He was feeling unwell but he wasn't making a fuss about it. He was about to start a new treatment that was quite experimental and that had had some success in other people. He felt optimistic about it being able to prolong his life, hopefully in the belief there would be better and newer treatments that would come along."

News of his death prompted an outpouring of grief as tributes poured in from around the world. Responding to the messages of support and sympathy, in a post on Bowie's official Facebook page, his family expressed their gratitude to the singer's legions of fans, adding that they "welcome everyone's celebration".

It has been reported that Bowie was cremated shortly after his death. He is survived by his wife, Iman, and children Duncan and Alexandria.