I wonder if Magnus in the show is the norwegian king "Magnus the Good" mixed with Fairhair's son "Håkon the Good"
Håkon was raised in England and went on to be King of Norway after Fairhair. While Magnus was the first scandinavian royal of that name (named after Charlemagne) And they made a bit too much point about it to be coincidence. Both were raised in exile and went on to be kings.
On account of Fairhair. His son Eirik Bloodaxe might make an appearance.