My great great grandfather is supposed to have been born in Germany back in the early 1850s and moved to the UK where he became a naturalised British citizen in 1870 approximately.
But on Ancestry my DNA test does not show any German ancestry.
Perhaps he was not the father of my great grandmother ?
My great grandmother was born 9 months after my great great grandparents got married. My gg grandmother was only 16 when she married, her German spouse 7 years older. 
They remained married and had further children.