Margaret would be the last princess born to a reigning English monarch until the birth of  who's wife?
Elizabeth of York Elizabeth of York (11 February 1466 – 11 February 1503) was queen consort of England from 1486 until her death. As the wife of Henry VII, she was the first Tudor queen. She was the daughter of Edward IV and niece of Richard III, and she married the king following Henry's victory at the Battle of Bosworth which started the last phase of the Wars of the Roses. She was the mother of King Henry VIII. Therefore, she was the daughter, sister, niece, wife, mother, and grandmother of successive kings and queens of England.
Princess Sophie of the Netherlands Princess Sophie of the Netherlands (Wilhelmine Marie Sophie Louise; 8 April 1824 – 23 March 1897) was the only daughter and last surviving child of King William II of the Netherlands and of his wife Grand Duchess Anna Pavlovna of Russia. She was heir presumptive to her niece, Queen Wilhelmina of the Netherlands, for seven years, from the death of her brother until her own death.