alright this is 'the' MacDuff, fictionally immortalized by Shakespeare.
what a can of worms in the mass of misinformation out there!
wikipedia Clan MacDuff makes him the son of Malcolm III (not possible) and so do a number of clan history websites.
one clan history website even claims extra legitimacy for Malcom III by having him marry Gruoch when he seized the throne!
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What do we actually know about this man?
1. he is certainly of scots royal blood somehow.
2. he is kinsman of Macbeth, Gruoch and Malcolm III.
3. the kinship is by females in the MacAlpin line of descent.
what else can he added here?
apparently, this explains some of the confusion over him being son of Malcolm III which he is not, sloppy reading will have resulted in conflating Áedh with ths man:
https://en.wikipedia.org/wiki/Ethelred_of_Scotland
The issue is that the Macduffs of Fife can be traced back as far as Gille Míchéil MacDuff, Earl of Fife -- the paper trail for taking the line back isn't there.
A fairly safe site for seeing what we actually have evidence for (as opposed to what we have stories about) is here -- http://fmg.ac/Projects/MedLands/SCOTLAND.htm#_Toc209085741
enjoy.
Gillemichel looks like he needs a clean up - just working with lousy internet today - it will be the bloody undersea cable to Africa that a shark or something has bitten again :-) :-/
See also https://www.geni.com/projects/Macbeth-Historical-Context-of-Shakespeare-s-Play/6078 and https://www.geni.com/projects/Shakespeare-s-History/39835