I always think 'Bertie' is a shortened version of Albert.
My DS is called Ben (his name is Benjamin, but he's never used it). To be fair, it was the only name that his dad & I agreed on (I wanted Max). I was being bullied by overbearing ILs, around the hospital bed, I was young, tired & wanting to BF, so I just agreed to the best name. He looks like a Ben now.