Quebec friend said de' means from or of. Maybe it was the name of a town, or a father. At one time there were no
surnames it was Tom the son of Tom the miller who later adopted Miller as a surname.
I looked it up too. An eg. was
Warren from France had a castle by the River Vareen so in France was called William of Varenne, went to England
and spelling changed to English Warenne in the Middle Ages.
I heard or read that Henry the VII is the one who wanted surnames - a pbs documentary?