What is fifty-stone? Since this is a children book with pretty much everything made up, I suspect this is also a made up term. But for the life of me, I just can't picture what an opera singer must look like to be described as being "fifty-stone."The longest recorded number two took four whole days to deliver. It was by fifty-stone opera tenor Antonio Lasagnotti. It was the length of a football pitch.
Source: Bad Dad - David Walliams - eBook