Queen Elizabeth (C), Prince Philip (2L), and Prince Charles (R), prepare to pose for a regimental photograph at Windsor Castle, April 30, 2015
London (AFP) - The birth of a princess on Saturday demonstrated the enduring strength of Britain's rulers, consolidating four generations of a family now more popular than ever, but cannot hide the weaknesses of an ageing institution.
Queen Elizabeth II turned 89 just weeks ago and shows no sign of abdicating, even if she has stepped back a little from public duties in favour of her 66-year-old son and heir Charles, the Prince of Wales.
Prince William and his wife Kate's second child will be fourth in line to the throne after Charles, William, and his first-born George -- a strong dynasty that could continue for another century.
Congratulations have flooded in for the parents, the glamorous Duke and Duchess of Cambridge who have helped give the Windsor family a modern makeover.
The new princess will be the first to benefit from a new law ending the age-old bias favouring a male succession, meaning that she cannot be passed over in favour of any younger male siblings.
The legal change has helped bring the royals into the 21st century but there is only a slim chance that she will ever wear the crown, in a family where the future is dominated by the older generation.
- 'Stuck with elderly monarchs' -
If the queen lives as long as her mother, who died aged 101, Charles would be about 80 when he finally takes the throne -- hardly the image of a young and vital monarchy.
"And if the Prince of Wales lives a long time, then William will also be quite elderly when he succeeds," said Bob Morris, a constitutional expert at University College London.
"Without some policy and application then we are going to be stuck with elderly monarchs for quite long time."
On September 9, the monarch will eclipse Queen Victoria to become Britain's longest-reigning monarch.
Buckingham Palace has emphasised her longevity as a virtue, presenting her as a stabilising influence and celebrating her Diamond Jubilee in lavish style in 2012.
There are few signs that she would consider quitting.
"I never rule out the idea of abdication but I think it's unlikely", Morris said.
However, he said the rise of Scottish nationalism that threatens the future of the United Kingdom will only have reinforced her desire to stay on.
Royal commentator Robert Jobson noted that Pope Benedict XVI and Spain's Juan Carlos have both retired from what were previously thought to be lifetime roles.
"I don't know if the queen will continue until the day she dies. I'm sure it's her intention but we are in uncharted territory," he said.
- Transition to Charles -
For now, the queen continues to reign as always, although her schedule and that of her 93-year-old husband Prince Philip have been slowly eased.
She will pay a state visit to Germany in June and attend a Commonwealth summit in Malta in November, but Charles and his sons are increasingly taking on her official duties.
Many commentators predict a slow period of transition of power to Charles.
A 1937 law allows for the heir to become a regent in the event of the monarch's physical or mental incapacity, Jobson said, although at the moment "there's no need to".
But while Charles awards medals and gives speeches, he "won't be able to carry the full range of monarchical duties", Morris pointed out.
"He could relieve her but he cannot replace her."
The queen remains hugely popular, although Charles' approval ratings fall below those of his mother and indeed his son.
A recent ComRes survey for the Daily Mail newspaper found that 79 percent of respondents liked William, compared to 77 percent for the queen and 53 percent for Charles.
Just 19 percent said they wanted to get rid of the monarchy, suggesting that for all the Windsor's problems, a republican revolution looks some way off.