Thanks for the quick reply. I was confused by the "guest cottage" advertisements that came up when I searched but you have cleared that up for me. I really appreciate that.
Yes, we were aware that my grandfather was illegitimate. We also had very little information about his mother and other family members but I took a chance on this birth certificate when I saw his name and Llangadfan in the FreeBMD index for around the time he was born. The only thing that doesn't match exactly is the certificate says his birth date is april 13 but on his passport and other paperwork he had april 15. I know he was living with his grandmother in 1891 and that maybe over time he came to believe the date was the 15th. What do you think?