The 36-year-old South African former Olympic swimmer and her 56-year-old husband, whom she married in 2011, issued a statement expressing their “immense joy” at the prospect of becoming parents together.

The short statement said the baby is due before the end of the year, meaning the princess is at least three months pregnant.

The news is sure to please the palace and will hopefully end the tabloid speculation that has dogged the relationship. Questions have been asked as to why, after nearly three years of marriage to Albert, Charlene had not yet provided an heir to the jet-set European principality.

Until the baby is born, the next in line to the throne of Monaco, a tiny fiefdom smaller than New York’s Central Park, is Princess Caroline, Albert’s older sister. The constitution was changed to allow Caroline a claim during Prince Albert’s tenure. This came about because after years of Albert’s high-profile affairs with numerous beautiful, famous women including Brooke Shields, Claudia Schiffer and Naomi Campbell, the kingdom’s subjects were concerned that he would never produce an heir .

Albert already has two children, both born out of wedlock and thus excluded from the succession – a daughter Jazmin Grace Grimaldi, and a son Alexandre Coste Grimaldi.

This baby news is sure to consolidate the couple’s place in the public eye – in positive ways this time – and how Charlene dresses to show off her royal bump is likely to set off a frenzy in the fashion press.

The demure South-African born princess is known for her elegant style, patronising designers such as Giorgio Armani, who designed her wedding gown.

Charlene’s full title is Her Serene Highness The Princess of Monaco. The previous holder of the title was her mother in law, the famously beautiful American, Grace Kelly, who died in a car accident in 1982.

– Sapa