ok, i found this on the net...so this does now prove that draco and harry were related: -
According to the Black family tree, one Charlus Potter married a Dorea Black, and together, they had a son.
Based on the timelines given by Rowling, it is most likely that Charlus Potter was the brother, or cousin, of Fleamont Potter, who was Harry’s paternal grandfather, and James Potter I’s father.
This would make Charlus the uncle or cousin of James Potter I, or the great-uncle (“grunkle”) of Harry himself. Charlus’s wife, Dorea, by extension, would be Harry’s great-aunt (“grauntie”).
It would also make Charlus and Dorea Potter’s son - whose name has never been revealed - Harry’s “first cousin, once removed”. Had he lived, he would’ve most likely been around Sirius Black’s age during the books’ timeline.
In turn, Dorea Black (Potter), by blood, was the great-aunt of Sirius Black (III) and Regulus Black (II), as well as Bellatrix Black (Lestrange), Andromeda Black (Tonks), and Narcissa Black (Malfoy).
As well as this, Dorea Black (Potter) is the great-great aunt of Draco Malfoy and Nymphadora Tonks (Lupin), and the great-great-great aunt of Scorpius Malfoy, James Potter II, Albus Potter, Lily Luna Potter, and Teddy Lupin.
So Draco Malfoy and Harry Potter both share the same great-aunt - Dorea Black (Potter) - by marriage.