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A queen mother is a dowager queen who is the mother of the reigning monarch (or an empress mother in the case of an empire). The term has been used in English since at least 1577. It arises in hereditary monarchies in Europe and is also used to describe a number of similar yet distinct monarchical concepts in non-European cultures around the world.

"The Queen Mother" usually refers to Elizabeth The Queen Mother, 1900–2002 (queen, 1936–1952; queen mother, 1952–2002), who was the mother of Queen Elizabeth II, and held the status of queen mother for 50 years.

A widowed queen consort, or dowager queen, has an important royal position (regardless whether or not she is the mother of the reigning sovereign) but does not normally have any rights to succeed a king as monarch on his death unless she happens to be next in line to the throne (one possibility would be if the King and Queen were also cousins and childless, the King had no other siblings, and she in her other position as his cousin was also his heiress presumptive).

A new reigning king would have (at accession or eventually) a wife who would be the new queen consort; and, of course, a queen regnant would also be called 'queen'. More to the point, there may be more than one queen dowager at any given time.

The title "queen mother" evolved to distinguish a queen dowager from all other queens when she is also the mother of the reigning sovereign. Thus, upon the death of her husband, George V, Mary of Teck became queen mother, retaining the status throughout the reigns of her sons, Edward VIII and George VI.

The title also distinguishes former queen consorts from those who are simply the mother of the current monarch. For example, Princess Victoria of Saxe-Coburg-Saalfeld was "the Queen's mother" when her daughter Victoria became queen regnant, but she was not "queen mother." It should be noted, however, that the title in British usage is purely a courtesy title. Whereas the wife of a king is called "queen", there is no constitutional or statutory recognition of "Queen Mother" as a title.

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