Where does the surname Grealis originat from?

Question:

Where does the surname Grealis originat from?

Best Answer - Chosen by Asker: Meaning of Grealis
Origin of the Surname:

From THE SURNAMES OF IRELAND by Edward MacLysaght, Irish University Press, 1973, (Mac) Grealish Mag Riallghuis , A Connacht form of MacNelis. In Ulster it sometimes takes the form MacGrellis or MacGrillis.

The above is the only reference I have found close to the surname Grealis. However, a story was told to me that during World War II, a Grealis from Co. Mayo was working in London and found it necessary to visit a first aid station during an air raid. The Norwegian doctor who assisted him said that he knew people by the name of Grealis in Norway. Perhaps some were shipwrecked on the coast of Ireland and were absorbed into the population.

I am also aware that in Galway the name is spelled Grealish.

I would welcome input from anyone researching the Grealis name anywhere in the world