As well as celebrating his milestone birthday, and inheriting £10million pounds left to him by his mother Princess Diana, Harry has his Army duties to occupy him, and has been heavily involved in the forthcoming Invictus Games for injured servicemen and women.
He is also involved in a number of charities, including Sentebale, which was co-founded by the Prince, and works to support orphaned children in Africa.
As a sibling to Prince George, the Duke and Duchess of Cambridge's second child will also not be expected to be crowned sovereign.
But second-born royal children - often dubbed the 'spare to heir' - have on occasion ended up as monarch.
The country's last king, George VI, was not meant to accede to the throne and only did so when his older brother Edward VIII abdicated over his love for American divorcee Wallis Simpson in 1936.
George VI's father, George V, was also not destined to wear the crown. But he outlived his older brother the Duke of Clarence and Avondale - Prince Albert Victor - who died from flu in 1892. George V became king in 1910.
William and Kate's new baby will be a great-grandchild to the Queen and a great-great-great-great-great-grandchild of Queen Victoria.
When Prince George was born on July 22, last year, he automatically became third in line to the throne of Britain and 15 other Commonwealth nations, following his father the Duke of Cambridge, and grandfather the Prince of Wales.
He is likely to take the throne as King George VII around the end of the century - although previous monarchs have not been averse to changing their name, such as the Queen's father, who was known as Bertie, but who ruled as George VI.
The new baby will also push Prince Andrew down to sixth place, followed by his daughters Beatrice and Eugenie in seventh and eighth.
Prince Edward goes into ninth, with his children Viscount Severn and Lady Louise Windsor in tenth and 11th. Even though Louise is older, the changes to the law of succession are not being applied retrospectively.
The most recent royal baby, Mia Tindall - the daughter of Zara Phillips and Mike Tindall - will become 17th in line to the throne. She does not bear a royal title.
The baby will be a prince or princess thanks to the Queen, who stepped in ahead of Prince George's birth to ensure all William's children would become HRHs with fitting titles.
The Queen issued a Letters Patent under the Great Seal of the Realm in December 2012 when Kate was just a few months' pregnant, declaring "all the children of the eldest son of the Prince of Wales should have and enjoy the style, title and attribute of royal highness with the titular dignity of prince or princess prefixed to their Christian names or with such other titles of honour".
A Letters Patent in 1917, issued by George V, limited titles within the royal family, meaning a daughter born to William or Kate would not have been an HRH but Lady (forename) Mountbatten-Windsor instead and a second-born son would also have lacked the HRH title and become Lord (forename) Mountbatten-Windsor rather than a prince.
William's cousin Princess Eugenie, who was born in 1990, was the last royal baby to be given the title Princess. The Earl and Countess of Wessex's daughter Lady Louise Mountbatten-Windsor is also technically a princess, but her parents decided, with the Queen's agreement, that she would use the courtesy title of the daughter of an Earl instead.
If the baby is a girl, it will be the first time a great granddaughter of a still-serving sovereign has been born in direct succession on the male line since 1897, when George VI's sister Princess Mary was born.
- Daily Mail
