He's been speaking to Premier as he launches a new album of hymns and popular songs with Songs of Praise presenter Aled Jones.
Talking about his battles with cancer, he said: "One thing which it did change profoundly was my faith.
"There's two ways which you can go with faith when you go through difficult and trying times - you can move away from faith and think 'why me?' or it can draw you closer to faith.
"Mine was the latter and I felt closer to God and was drawing on that strength that was coming from something spiritual to help me get through that difficult period."
Watson was diagnosed with having a pituitary tumour in 2005 and again in 2007.
The singer has received numerous awards and chart success through his music.
His new album with Aled Jones is called In Harmony and features hymns like How Great Thou Art and more modern worship songs like In Christ Alone.
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