Prince Albert II of Monaco and his wife Charlene have welcomed their twin babies Gabriella and Jacques to the world, as cannons roared and church bells tolled in the tiny Mediterranean principality.
Despite being born two minutes after his sister, Monaco's succession laws mean Jacques is next in line to head the 700-year-old House of Grimaldi.
Gabriella Thérèse Marie was born at 5.04 pm on Wednesday followed by Jacques Honoré Rainier at 5.06 pm, the palace said in a statement, adding that the newborns and their glamorous South African mother were "doing well".
The babies replace Albert's sister Caroline as heirs to the throne, and will likely draw a line on rumours of the royal couple's supposedly rocky relationship.
The prince's late father, Rainier III, had rewritten the constitution as he became ill in 2002 so one of his daughters could inherit if his son - who had fathered two children out of wedlock - failed to produce a legitimate heir.
But Albert, 56, finally married former Olympic swimmer Charlene, 36, in 2011 - 11 years after the pair first met.
The birth of the twins at the hospital named after their grandmother Princess Grace was celebrated with 42 cannon shots, 21 for each child, fired from an old fort overlooking the sea.
Church bells also rang out for 15 minutes, followed by boat horns, as Monegasques toasted their future absolute rulers.
The gender of the twins had been kept a secret during Charlene's pregnancy, even from their father who said he wanted to be surprised.
Albert - whose late mother was Hollywood star Grace Kelly - had earlier said that if the twins were a boy and a girl, it would be the boy who would succeed him.
According to tradition, an official birth announcement, signed by Albert, will be displayed at the entrance to the palace and the public will be invited to sign a book of congratulations.
Monegasques have also been encouraged to fly the principality's red-and-white flag from their homes until the day the twins are formally presented to the nation by the royal couple from the palace balcony.
Albert, who was once considered one of the world's most eligible bachelors, succeeded his father Prince Rainier in 2005 at the age of 47.
He already had a daughter, Jazmin, 22, after a fling with an American former waitress Tamara Rotolo. He denied being her father for years before DNA tests proved otherwise when she was a teenager.
The prince also has a younger son, Alexandre Coste, 11, from an affair with Nicole Coste, a Togolese former Air France hostess.
Under Monaco's inheritance laws, neither of them have any claim to royal titles or to be considered as heirs to Albert because they were born outside of marriage.
They do however have legal rights to a share of his huge personal fortune, estimated by Forbes magazine to exceed one billion dollars.
Monegasques gathered outside the palace late on Wednesday, which was lit up in red lights for the occasion, and waved flags to celebrate the births.
For Fabienne Guenoune, president of the Le Rocher residents' association, "the 42 cannon shots announcing the birth seal more than ever the future of the country".
"A boy and a girl, it's the wish of a king," added Michele Mattoni, another resident of The Rock, as Monaco is also known.
"This is an explosion of joy for all Monegasques," said Marguerite-Marie Bergonzi, who comes from one of the oldest families in the world's second smallest independent state.
Zimbabwe-born Charlene tied the knot with Albert three years ago despite rumours that their relationship was on the verge of collapse.
Media reports suggested she had attempted to flee Monaco just days before their wedding.
It was also widely reported that the couple spent at least part of their honeymoon in separate hotels. A steady stream of pictures of the princess looking gloomy continued to fuel reports she was depressed.
The royal births are the latest addition to the Grimaldi baby boom, with Princess Caroline becoming a grandmother twice over since 2013.
The royal family's tumultuous private life has made it a staple of celebrity magazines for decades, with Caroline's daughter Charlotte continuing the tradition with her relationship with the comedian Gad Elmaleh. Their son Raphael was born last December.
Crown Prince Jacques will receive the title of Marquis of Baux, while his sister, second in line to the throne, will be the Countess of Carlades.