NICE -- Hollywood golden couple Brad Pitt and Angelina Jolie are the proud parents of new-born twins, a boy named Knox Leon and a girl called Vivienne Marcheline, the hospital announced Sunday.

Jolie, 33, gave birth to the twins on Saturday evening during a half-hour caesarean operation at a maternity clinic in Nice on the French Riviera.

"Everything went smoothly. The children are doing very well, the mother is doing very well and the father is doing very well," gynecologist Michel Sussmann told AFP.

Knox Leon weighed 2.27 kilos (five pounds) and Vivienne Marcheline 2.28 kilos.

Pitt, who had already attended the birth by caesarean of their daughter Shiloh, "was very calm and was not at all disturbed" by the operation, said Sussmann.

"When the babies arrived he was very euphoric" and Jolie had a "blinding smile", he added.

Jolie is set to stay several more days at the Fondation Lenval clinic to recover. The twins were born slightly earlier than scheduled, Sussmann said.

"For a caesarean the length of stay varies between five and seven days. But since these are twins, and they were born a bit early, the stay might be a bit longer," Sussmann said.

Mayor of Nice Christian Estrosi went to the hospital on Sunday afternoon to complete the necessary paperwork for the twins. As he left, he showed the documents to the waiting photographers and cameramen.

The first photograph of the baby celebrities was sold to a US paper for $11 million (?6.9 million), the regional Nice-Matin newspaper said, adding that the money would be given to a humanitarian cause.

The twins brought the number of Jolie's children with 44-year-old Pitt to six.

Dubbed "Brangelina" in the press, the couple have adopted three children: Maddox, six, born in Cambodia; four-year-old Pax, born in Vietnam; and Zahara, three, born in Ethiopia.

Their first biological child, Shiloh, was born May 2006 in Namibia.

In May, the pair set up home in a chateau they rented from an American acquaintance in France's Provence region.

The couple, who met while filming "Mr. and Mrs. Smith" in 2005, have seen their relationship flourish despite frenzied tabloid attention and relentless speculation about a possible split.

Award-winning actress, Jolie is the daughter of actor Jon Voight. She began her meteoric rise to stardom when she took home an Oscar for best supporting actress in 1999's "Girl, Interrupted."

In addition to her movie career and founding a family with Pitt, she works as a goodwill ambassador for the UN High Commissioner for Refugees.

Both Pitt and Jolie top the list of highest paid Hollywood stars, making $10-20 million a film.

In April 2006, Oscar-winner Jolie was crowned People magazine's most beautiful person in the world, while Pitt has claimed the male crown twice. They remain coy about whether they ever plan to marry.

"People have made a lot out of it that we're not," twice-divorced Jolie told a recent interviewer. "But we both have been married before, and it's very easy to get married, but it's not easy to build a family and be parents together.

"Any maybe we've done it backwards, but we certainly feel married."