
Upon the accession of Queen Victoria in 1837, Mary Adelaide’s family returned to England.
Princess Augusta of Cambridge, Grand Duchess of Mecklenburg-Strelitz (1822 – 1916), married Friedrich Wilhelm, Grand Duke of Mecklenburg-Strelitz, had issue. Prince George, Duke of Cambridge (1819 – 1904), married Sarah Louisa Fairbrother, had issue (marriage was in contravention of the Royal Marriages Act so it was not legal and children of the marriage were illegitimate). Mary Adelaide had an older brother and an older sister: Princess Friedrich Augustus of Anhalt-Dessau (born Princess Marie Luise of Hesse-Kassel, her maternal first cousin). Princess Elizabeth, Landgravine of Hesse-Homburg (her paternal aunt).
Grand Duchess of Mecklenburg-Strelitz (born Princess Marie of Hesse-Kassel, her maternal aunt).
Princess Mary, Duchess of Gloucester (her paternal aunt). Queen Adelaide (her paternal aunt by marriage). She was named Mary Adelaide Wilhelmina Elizabeth for her godparents. The infant princess was christened on January 9, 1834, at Cambridge House in Hanover by Reverend John Ryle Wood, chaplain to her father. She was born on November 27, 1833, at Cambridge House in the Kingdom of Hanover where her father served as Viceroy of Hanover for his brothers King George IV and King William IV, who were also Kings of Hanover. Princess Mary Adelaide, the youngest of the three children of Prince Adolphus, Duke of Cambridge (the seventh son and tenth child of King George III and Queen Charlotte) and Princess Augusta of Hesse-Kassel.
Through her daughter Mary (known as May), Mary Adelaide is the great-grandmother of Queen Elizabeth II of the United Kingdom and an ancestor of the members of the House of Windsor. Princess Mary Adelaide of Cambridge was a male-line grandchild of King George III of the United Kingdom, a first cousin of Queen Victoria of the United Kingdom, and the mother of Mary of Teck, wife of King George V of the United Kingdom.