Relationships between George V, Wilhelm II, and Nicholas II?

Nicholas' mother was the sister of the wife of Edward VII, who was mother of George V. So Nicholas and George V were first cousins through a different line of descent than that which made George V, Wilhelm II and Alexandra first cousins by descent from Victoria.

Nicholas was the son of Emperor Alexander III and Empress Maria Feodorovna of Russia, the latter of whom was born "Princess Dagmar of Denmark". Her father was Prince Christian of Schleswig-Holstein-Sonderburg-Glücksburg and her mother was Princess Louise of Hesse-Cassel. Her sister, Princess Alexandra Caroline Marie Charlotte Louise Julia, or "Alix", married Edward VII, and was mother to George V.

George V and Wilhelm II both shared Queen Victoria as a grandmother; George's father was Edward VII (Victoria's son) and Wilhelm II was Princess Victoria's son (Queen Victoria's daughter who married the German Emperor). George V and Nicholas II were cousins as well, but it was through George's mother that they were related; not his father. George's mother was Queen Alexandra (born a Danish Princess), her sister Maria married Nicholas the 2nd's father, Emperor Alexander. So, George's father's sister was Wilhelm's mother and George's mother's sister was Nicholas's mother. So, one was a cousin through his father and the other through his mother. Of course the Russian royals are gone but the Danish royals aren't; in fact there were two more marriages between the British family and the Danish: Prince George, the son of George V and the current Queen both married people from the Danish royal house.

Queen Victoria of Britain, actually.