LONDON (Reuters) - The newest member of Britain's royal family, due to make an entrance this month when Prince William's wife Kate gives birth to the couple's second baby, will be taking on one of royalty's toughest roles -- life as "spare to the heir".
Unlike brother George, born 21 months ago and expected one day to be monarch, the younger offspring's future is less clear.
The "spare" role is an undefined one that allows more freedom than that accorded to a future king or queen.
But it also attracts massive public interest and scrutiny, while the possibility remains of having to step into the shoes of the future heir should calamity befall the elder sibling.
"I think the most difficult thing about being the number two is you don't know if by some misfortune you are going to be called upon to take the number one role," royal historian Hugo Vickers told Reuters.
"You never quite know if you're going to be called upon to become king, or instead have what you, if you're being really cynical, could say is a relatively pointless life."
Both the queen's grandfather George V, whose elder brother died aged 28, and her father George VI, whose elder brother Edward VIII abdicated to marry American divorcee Wallis Simpson, were "spares" who did become monarchs.
For those for whom the top job never comes, life as a "spare" is not easy.
"It's incredibly difficult for the younger sibling," said Claudia Joseph, author of "William and Kate's Britain".
Princess Margaret, the queen's younger sister, who died in 2002, was a prime example.
Renowned as a beauty in her youth who partied with a high society set, her private life generated intrigue for the media. She is best remembered for falling for dashing air force officer Peter Townsend when protocol dictated that a princess could not marry a divorced man.
Instead she later married photographer Anthony Armstrong-Jones, a controversial choice because of his non-aristocratic status.
They divorced in 1978, in the first such split in the inner royal circle since the days of King Henry VIII.
William's brother Prince Harry too is stuck with the "spare" role.
He won a reputation as a wild child by dabbling with marijuana and under-age drinking, clashing with paparazzi outside nightclubs and wearing a Nazi uniform to a costume party.
Before his second tour of duty in Afghanistan in 2012, the 30-year-old was pictured naked cavorting with an apparently nude woman in Las Vegas. But through all such troubles, his popularity has actually increased.
Prince Andrew, younger brother of current heir-to-the-throne Prince Charles, has also had a tricky time with the media. The former naval officer earned the nickname "Randy Andy" for his wooing of models and starlets, famously dating actress Koo Stark who had appeared in a soft-porn film.
Like Prince George, the world's media is set to lavish attention on William and Kate's new baby. But commentators believe the relatively down-to-earth couple are better placed than previous generations to help their child cope.
"The new girl or boy will have more opportunities because he or she's not going to be brought up in the same gilded lifestyle," said royal biographer Joseph.
Reporting by Michael Holden; editing by Andrew Roche