By tradition, male members of the Royal family receive a title from the monarch on their wedding day, and the vacant title Duke of Sussex was regarded as the most likely choice for the Prince.
The only previous Duke of Sussex, George III's sixth son Augustus Frederick., was married twice, but neither of his marriages was approved by his father, meaning they were considered unlawful.
A dukedom is the highest rank in the British peerage and comes from the Latin word dux, meaning leader.
Traditionally, the monarch would bestow these titles on people loyal to the crown, in exchange for land or money, or they were inherited from a direct ancestor. They were known as "peers of the realm".
The five titles, from highest to lowest are: duke, marquess, earl, viscount, and baron for men; duchess, marchioness, countess, viscountess, and baroness for women.
Like Prince Harry, the previous Duke of Sussex, Augustus Frederick, lived at Kensington Palace, and he also married for love, rather than choosing brides who fitted the traditional royal mould.
Prince Augustus Frederick was not given consent by his father, King George III, to marry his first wife Lady Augusta Murray, as she was considered to be from too low a social rank.
The Prince married her anyway, in secret in Rome in 1793, and then again in England when they returned, but without the king's permission the marriage contravened the Royal Marriages Act 1772 and was annulled in 1794.
The couple continued to live as man and wife and had two children before they eventually separated.
When Prince Harry's brother William married Catherine Middleton in 2011, the Queen bestowed the title of the Duke of Cambridge, Earl of Strathearn and Baron Carrickfergus on her grandson. Catherine, known as Kate, became the Duchess of Cambridge.
