“All kingdoms are monarchies but not all monarchies are kingdoms.”
Queen Elizabeth’s husband [late husband] Prince Philip [was] related to the Romanovs through both his mother and his father. Philip is the grandnephew of Alexandra Romanov, Nicholas II’s wife, and the last Tsarina of Russia. He is also a cousin to the Russian royal family.
Philip’s children and grandchildren, including William and Harry, are therefore related to the Romanovs as well.
In fact, when the remains of two children thought to be Maria and Alexei Romanov were found in a field in 2007, it was Prince Philip’s DNA that was used to identify them, news which was revealed in 2016. – Town & Country
How is Queen Elizabeth related to other European monarchs?