I don’t see the Earl of Northumberland as having anything to do with the de Ports. Or with the lady of Semer. It’s a jump up story in the Percy pedigree.
https://en.m.wikipedia.org/wiki/Ethelreda,_daughter_of_Gospatric
Ethelreda (either the same as or conflated with Octreda or Uhtreda; 11th century) was a daughter of Gospatric, Earl of Northumbria remembered in 13th century Cumberland as the mother of William fitz Duncan. She is thought to have been the wife of Duncan II of Scotland, though very little is known otherwise about her.
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The Queen of Scotland and a Kent sheriff? Nah.