Doctors are aiming to slow the spread of the illness, but will not know if Sir John is responding to treatment until July.
He has started a three-month course of radiotherapy at Newcastle’s Freeman Hospital.
Sir John Hall: “From the first moment I was told it’s got outside the gland, and they did a biopsy, to see how bad the cancer was.
“I wanted a second opinion, so I went and saw a specialist and he said you’ve got it. He did some more tests and when the results came back it was 9.5 on a scale of 10 and it was aggressive and it had got outside the prostate gland. It has got into my bones, it’s in my pelvis.
“When you find out it’s like a bolt out of he blue, it’s like an exocet hitting you. It was such a blow.
“I was a novice of what prostate cancer was so I went on the internet, I can use it to the extent of typing in prostate cancer.
“There’s many, many pages, very good web pages if people want to read them, Macmillan and cancer charities.
“Men out there need to take my advice, if you have any concerns, or any symptoms, if you’re getting up in the night for the toilet, go and see your doctor. You need to catch it early.”