Question about DNA testing and identifying illegitimate children

[OnlyTeaForMe]

This is partly out of personal interest, but also because we have a family story about a relative being born in 1815 as the illegitimate son of rich bloke and one of his servants and then adopted 200 miles away into our family.

Q: If a family group has always been concentrated in one part of the country e.g. Scotland and someone whose father was European and mother SE England was then adopted into that family, could anything show up in DNA testing 200 years later to arouse suspicion?

Sorry, also meant to say - I am trying to write a short story about this and want to see if I have any grounds for a character 'suspecting' his great, great grandfather's parentage.

I already know that adoption records weren't routinely kept until much later.

I think most autosomal dna tests go back about 8 generations? 23andme do a little ancestral timeline which I found surprisingly accurate, something like that? Some regions seem to have stronger genetic communities than others so I guess it depends whereabouts in Europe.