Why was the Prince of Wales, during the Napoleonic Wars, reffered to as "The Dutch Bastard"?

You are probably thinking about "Prinny", the Prince of Wales during the overly long reign of George III, and who eventually became George IV.

The Hanoverians, starting with George I in 1714, were never popular kings of England. The first George never learned English very well and was often referred to as "that German bastard" or that "Dutch Bastard' [mispronunciation of "deutch", meaning German].

William I was the illegitimate son of Robert I the Devil, Duke of Normandy, and Arletta, a tanner's daughter. Before going on pilgrimage in 1034, Robert obtained recognition of William as his successor, but a period of anarchy followed Robert's death in 1035. As he grew up, Duke William gradually established his authority; his victory over a rival at Val-ès-Dunes in 1047 made him master of Normandy. One chronicle relates that in 1051 or 1052 he visited his childless cousin king Edward the Confessor of England, who may have promised him the succession to the English throne.

thats the first time i have heard him called,i think you have the wrong period.