In use since 1189 at the latest
Blazon: Gules two lions passant guardant or armed and langued azure
Oh, Normandy. Never change. You haven’t since like, 1189 at the latest, but we already saw what happened to Aquitaine, so. And I do say 1189 instead of 1066, because we don’t have any contemporary records of William the Conqueror using the two lions. The number of lions was a little flexible for a while, but it was pretty solidly established as two by the fourteenth and fifteenth centuries.
I will also take this opportunity to point out the issue with the leopards. The position of “passant guardant” in English heraldry is blazoned as “leopardé” in French. Often, from translation errors, confusion, or laziness, this results in lions passant guardant being recorded in English as leopards. This problem is especially acute in regards to the Norman coat of arms, which a. actually has lions passant guardant, and b. belongs to a region that kept switching back and forth between France and England for a while. If you ever see an English reference to the leopards of Normandy, it’s technically incorrect, but a very common and understandable error.