Friday's civil wedding will be followed a day later by a religious ceremony at the royal palace on the Mediterranean.

Ms Wittstock, 33, who swam in the 2000 Sydney Olympics, will become Her Serene Highness, Princess Charlene.

The palace has denied reports in the French press that Ms Wittstock was getting cold feet about the wedding.

The guest list includes heads of state and royalty, from French President Nicolas Sarkozy to the heir to the Spanish throne, as well as fashion designer Karl Lagerfeld and supermodel Naomi Campbell.

Charlene Wittstock will wear a Giorgio Armani gown. The couple will then proceed to the nearby chapel of Saint Devote, the patron saint of Monaco, where Ms Wittstock will leave her bouquet.

But the event has been clouded by press reports suggesting that Ms Wittstock had come close to returning to South Africa, after learning secrets about Prince Albert's private life.

The royal family dismissed the claims, as well as suggestions she had only turned back after royal aides persuaded her to stay.