He grew up and when he heard he was adopted he was told by his new parents his original birth name. When he recieved his birth certificate recently the name on his birth certificate for birth mother , was different to what he was told by his adopted parents.Therefore it is assumed it was his grandmother as he was told what his grandparents names were when younger.
Not checked the electoral registers as wouldnt that only show the Parents of the household??
Or is that me being dim??? lol