Prince Wilhelm of Prussia (Wilhelm Friedrich Franz Joseph Christian Olaf, 4 July 1906 – 26 May 1940) was the eldest child and son of Crown Prince Wilhelm of Germany and Duchess Cecilie of Mecklenburg-Schwerin. At the time of his birth, his grandfather Wilhelm II was the reigning Kaiser and he was second in line to the Prussian and German thrones. He was expected to one day succeed to the throne after the deaths of his father and grandfather, but the monarchy was abolished in 1918 at the end of World War I. Wilhelm was killed while serving in the German army during the Battle of France in 1940, while both his elders were still alive.
Some speculation is necessary, as Wilhelm IV is not actually stated to be the conqueror, nor is his precise identity stated. On the first point, the presence of his statue strongly implies that he was the conqueror. On the second point, at the time of the break-point this Prince was expected to someday inherit that numeral, so it can be reasonably assumed that this happened in the alternate.