Adelaide was born on 13 August 1792 at Meiningen, Thuringia, Germany. Her father was George I, Duke of Saxe-Meiningen; and her mother was Luise Eleonore, daughter of Prince Christian of Hohenlohe-Langenburg. She was titled Princess Adelaide of Saxe-Meiningen, Duchess in Saxony with the style Serene Highness from her birth until the Congress of Vienna (1814–15), when the entire House of Wettin was raised to the style of Highness.

Saxe-Meiningen was a small state, covering about 423 square miles (1,100 km²). It was the most liberal German state and, unlike its neighbours, permitted a free press and criticism of the ruler.

By the end of 1811, King George III was mad and, although still King in name, his heir-apparent and eldest son George was Prince Regent. On 6 November 1817 the Prince Regent's only daughter, Princess Charlotte, wife of Prince Leopold of Saxe-Coburg-Saalfeld (later King Leopold I of the Belgians), died in childbirth. Princess Charlotte was second in line to the throne: had she outlived her father and grandfather, she would have become Queen. With her death, the King was left with twelve children and no legitimate grandchildren. The Prince Regent was estranged from his wife, who was forty-nine years-old, thus there was little likelihood that he would have any further legitimate children. To secure the line of succession, Prince William, Duke of Clarence, and the other sons of George III sought quick marriages with the intent of producing offspring who could inherit the throne. William already had ten children by the popular actress Dorothea Jordan, but, being illegitimate, they were debarred from the succession.

...
Wikipedia