This Y-DNA is present in at least one modern lineage:
R-P312/S116 > Z40481 > ZZ11 > U152/S28 > Z56 > BY3548 > Z43/S366 > Z144 > BY28794 > PF6582 > PF6577 > FGC36902/BY3953 > FGC36897 > FGC36895 > A8380 > FGC41936
The families that have this (FitzRandolph and Randoll) are genealogically male-line descendants of Count Eudon Penteur (c999-1079), de facto Duke of Brittany from 1040 to 1057.
FGC41936 is estimated to be a 12th century mutation of A8380, which we would therefore expect to be Eudon's Y-DNA.
Eudons' children, the Eudonids, claimed descent from the Roman families Rutilius Rufus and Aurelius Cotta, specifically Rutilia, mother of Aurelia, mother of the dictator Gaius Julius Caesar.
Gildas's war-orphan hero Ambrosius Aurelianus's surname indicates that he was born an Aurelius but adopted into another (unnamed) family, just as Gaius Octavius was adopted by Julius Caesar and became Octavianus.
Some Aurelii were in Britain in the 200s as evidenced by the gravestone found at Carlisle of Aurelia Aureliana, wife of Ulpius Apolinaris.
That is particularly interesting as we know from a letter of Sidonius Apollinaris, dated before 470, that one of his friends was 'Riothamus', leader of the Romano-Britons in either Britain or Gaul or both.
Riothamus is a Latinised Brythonic title, probably meaning high king. It has been speculated that Riothamus is the same person as Ambrosius Aurelianus as they were contemporaries, performed similar roles, and both are described as exceedingly modest.
It is conceivable that Sidonius and Riothamus may have been related, through that 3rd century married couple who lived near the western extremity of Hadrian's Wall.
The Aurelii were a prolific family. Many Consuls and Emperors were Aurelii by ancient descent or by adoption. So it is not improbable for branches of the Aurelii to have descendants, even some male-line descendants, today.
The claim by the Eudonids of descent from the Aurelii is rendered plausible by their living male-line descendants' possession of ancient central Italian Y-DNA.
Had they fabricated any section of their long medieval or modern pedigree, or if non-paternal events occurred, it would be most likely for them to be R1b-L21, R1b-U106, I1 or I2, like the people who surrounded them during the many centuries they resided in Brittany, Normandy and England.