Why the Duke of Edinburgh is not king England?

Prince Philip, the Duke of Edinburgh and husband to Queen Elizabeth II, was never in line to the British throne. Under British constitutional law, which adheres to male-preference primogeniture, the order of succession to the throne is determined by descent from Sophia, Electress of Hanover, who was a granddaughter of King James I. According to this law, the throne passes to the eldest surviving child of the reigning monarch. If a monarch has no children or if all of their children are deceased, the throne passes to the next oldest sibling or their descendants.

Additionally, the Act of Settlement 1701 requires the British Monarch to be in communion with the Church of England. Prince Philip, being a member of the Greek Orthodox Church, did not meet this requirement and was thus not eligible to become King of England.