Stewart, 65, was diagnosed with thyroid cancer in 1990 and he was given an emergency operation to remove the cancer.
Speaking to UK newspaper Daily Mirror, he said: 'I was standing in my library when I got the call. At first I didn't panic because I just tried to focus on being positive.
'Everything seemed under control and everyone was telling me that it was easy to get rid of. I was lucky to have caught it in the very early stages.'
He added: 'I was taken into hospital and it was only when I was coming round from the op, that I was told that there was one problem. To get the cancer out they had to cut near a nerve that controls the voice box, the slightest slip would have meant I'd have lost my voice for good.
'As it was, the doctor told me that my voice wouldn't be back for three months. Three months came and went and it hadn't come back, then another three months and still nothing.'
Stewart then started pushing his voice more and more and 'screamed, swore and shouted as hard' as he could and his voice finally came back.