Actually it wasn’t my spoke. It was the nipple that holds the spoke to the rim. At first I was shocked but when I thought about it it makes sense. I looked it up on the web and found that it does happen.
My fear now is that there are others that are about to go. Being the anal retentive geek I am I have no choice but to disassemble the wheel and check each and every spoke and nipple. Maybe I’ll check the true while I’m at it. Might as well do the front wheel as well. Is this normal?