I thought it was Hardrada - Hard Counsel. But maybe that's my Anglo-Saxon talking.
Faulty mememor and folk etymology strikes me again. Yes OE and ON are very similar.
Wikipedia:
Harald III Sigurdsson (1015 – September 25, 1066), later surnamed Harald Hardråde (Old Norse: Haraldr harðráði, roughly translated as "Harald stern council" or "hard ruler")
Since I'm at it might as well correct something else, not Trygrvvson, but Harold Sigurdsson!