Births Jun 1871    Frowen  Frederick Albert     Chepstow vol 11a page 10 
so have you checked 1871 to see if the Frowens had an older son or daughter ?
The fact that he's surnamed Frowen implies a father so named, but very common for a family to take in an illegitimate child of a daughter, who would have implicitly given him her name (note there is nowhere on a Birth Cert that provides the surname of the child   

 )
I'll have a look at 1871 if you like, but the Cert will tell the story