Unfortunately it's not uncommon for tests for one type of cancer to reveal the presence of a different cancer too. It happened to me: the MRI scan for prostate cancer showed up an unrelated kidney tumour. I was fortunate in that both cancers were early stage, and surgical removal of my left kidney will (hopefully) have fixed that problem for good.
As John said, there's a whole array of treatment available for advanced prostate cancer, and every reason to believe you'll be with us for years yet.
Very best wishes,
Chris