Princess Mary Adelaide of Cambridge (Mary Adelaide Wilhelmina Elizabeth; 27 November 1833 – 27 October 1897) was a member of the British Royal Family, a granddaughter of George III. She later held the title of Duchess of Teck by marriage.

Mary Adelaide is remembered as the mother of Queen Mary, the consort of George V. She was one of the first Royals to patronise a wide range of charities.

Mary Adelaide was born on 27 November 1833 in Hanover, Germany. Her father was Prince Adolphus, Duke of Cambridge, the youngest son of George III and Queen Charlotte. Her mother was Princess Augusta, Duchess of Cambridge, the daughter of Friedrich III, Landgrave of Hesse-Cassel.

Mary Adelaide spent the early years of her life in Hanover, Germany, where her father acted as viceroy in place of her uncles George IV and later William IV. Her love of food and tendency to overeat led her to become seriously overweight, and to her subsequently being nicknamed "Fat Mary."

After the death of William IV, Mary Adelaide's cousin, Princess Victoria of Kent ascended the throne in 1837. However Salic law prevented Victoria from ascending the throne of Hanover, which instead passed to Prince Ernest Augustus, Duke of Cumberland. Thus, the Duke of Cambridge was no longer needed in Hanover, and returned to London with his family, setting up residence in Kensington Palace.

By the age of 30, Mary Adelaide was still unmarried. Her unattractive appearance and lack of income were contributing factors, as was her advanced age. However, her royal rank prevented her marrying someone not of royal blood. Her cousin Queen Victoria took pity on her, and attempted to arrange pairings.

Eventually a suitable candidate was found in Württemberg, Prince Francis of Teck. The Prince was of lower rank than Mary Adelaide, and was also the product of a morganatic marriage and had no succession rights to the throne of Württemberg, but was at least of princely title and of royal blood. However, with no other options available, Mary Adelaide decided to marry him. The couple were married on 12 June 1866, at Kew Church, Surrey.

Mary Adelaide requested that her new husband be promoted to the rank of His Royal Highness but was refused by Queen Victoria. He was, however, promoted to the rank of His Highness in 1887 to celebrate Queen Victoria's golden jubilee.

The Duke and Duchess of Teck chose to reside in London rather than abroad, mainly because Mary Adelaide was the only breadwinner for the Tecks. She received £5,000 per annum as a Parliamentary annuity for carrying out Royal duties. Her mother, the Duchess of Cambridge, also provided her with supplementary income. Requests to Queen Victoria for extra funds were generally refused. However, the Queen did provide the Tecks with apartments at Kensington Palace and White Lodge, Richmond as a country house.

Despite their modest income, Mary Adelaide had expensive tastes and lived an extravagant life of parties, expensive food and clothes, and holidays abroad. The debts soon built up and the Tecks were forced to flee the country in 1883 to avoid their creditors. They travelled to Florence, Italy, and also stayed with relatives in Germany and Austria. Initially they travelled under the names of the Count and Countess von Hohenstein. However, Mary Adelaide wished to travel in more style and reverted to her royal style, which commanded significantly more attention and better service.

The Tecks returned from exile in 1885 and continued to live at White Lodge in Richmond. Mary Adelaide began devoting her life to charity, serving as patron to Barnardo's and other children's charities.

In 1891, Mary Adelaide was keen for her daughter, Princess Victoria Mary of Teck (known as "May") to marry one of the sons of the Prince of Wales, the future Edward VII. On the other hand, Queen Victoria wanted a British-born bride for the future king, though of course one of royal rank and ancestry - not some "lowly" noblewoman. Mary Adelaide's daughter fulfilled the rank criteria. After Queen Victoria's approval, May became engaged to the second in line to the British throne, Prince Albert Victor, Duke of Clarence. The death of the Duke of Clarence only six weeks later looked like a cruel blow. However, Queen Victoria was fond of Princess May and persuaded the Duke of Clarence's brother, and next in the line of succession, Prince George, Duke of York, to marry her instead.

The marriage of May into the top rankings of the royal family led to a dramatic revival in the fortunes of the Tecks, with their daughter one day to be Queen consort. Unfortunately Mary Adelaide never saw her daughter as queen consort. Mary Adelaide died on 27 October 1897 at White Lodge, Richmond Park, Surrey, and was buried in the royal vault at St. George's Chapel, Windsor.

*27 November 1833 – 12 June 1866: Her Royal Highness Princess Mary Adelaide of Cambridge *12 June 1866 – 16 December 1871: Her Royal Highness Princess Francis of Teck *16 December 1871 – 27 October 1897: Her Royal Highness The Duchess of Teck

The Duke and Duchess of Teck had four children:

* List of British princesses

Cambridge, Mary Adelaide of Cambridge, Princess Mary Adelaide of Cambridge, Princess Mary Adelaide of