Brad Pitt was emotional but calm, Angelina Jolie laughed and chatted. The world's most famous celebrity couple were joined in emotion during the birth of their twins _ a boy and a girl _ and all "are doing marvelously well," the doctor who delivered the babies in a seaside hospital on the French Riviera said Sunday.

The newborns _ Knox Leon and Vivienne Marcheline, born one minute apart Saturday evening _ are the ultimate million-dollar babies, with experts estimating their first photos will fetch a fortune.

"In the celebrity world, it seems to be the double second coming," said Darryn Lyons, owner of Big Pictures, a photo agency in London.

For now, mother, father and newborns are resting out of the public eye on the fifth floor of the Lenval hospital, behind blue mirrored windows that provide sweeping views of Nice's sun-drenched beaches, but specially treated to deflect the prying lenses of paparazzi.

Jolie's obstetrician, Dr. Michel Sussmann, said the 44-year-old Pitt was at Jolie's side during the delivery, looking on as the doctor performed a Caesarean section to deliver Knox, weighing in at slightly over 5 pounds, and Vivienne, who weighed 5 pounds.

"He was my assistant," Sussmann joked.

"He was very happy. ... The emotion was very strong for him," Sussmann told reporters on the hospital steps. "I felt the emotion of both the mother and the father. Angelina Jolie was speaking, was laughing with her husband. They were happy."

"The mother, the babies, the father are doing marvelously well," he said.

Sussmann said the Caesarean was moved forward from its originally planned date "for medical reasons" so the babies could be born "in the best conditions." The doctor did not elaborate.

He said Jolie, 33, is expected to stay in the hospital for a few more days and that she now needs rest. The four other Jolie-Pitt children _ Maddox, 6; Pax, 4; Zahara, 3; and Shiloh, 2 _ have not yet seen their new sister and brother, he said.

The doctor said he believed the baby girl's middle name was chosen in honor of Jolie's mother, actress Marcheline Bertrand, who died in January 2007 after a 7 1/2-year battle with cancer.

News of the births attracted a small crowd of fans hoping to snap a photo of Pitt _ or any of their celebrity friends stopping by to pay a visit. None appeared, but the mayor of Nice delivered the twin's birth certificates, which he later displayed to reporters, with the family's approval, showing Pitt's scrawling WBP, for his full name William Brad Pitt.

"The father is having one of the happiest moments of his life, like any father, especially when they have the joy of having two children from such a wonderful wife as Angelina Jolie," Mayor Christian Estrosi said after the brief official visit, which spared Pitt the gauntlet of paparazzi that would accompany any trip to City Hall.

"The mother is doing fine. She is smiling a lot. She is as happy as the father," Estrosi said.

The twins' arrival has spurred a rash of speculation about the price of the first "official" snaps.

Nice Matin, the hometown daily in the Riviera city in the south of France, put the worth of the twins' photos at more than $11 million. It first broke news of the birth and reported Sunday that the couple have sold the rights for the first photo of their newly expanded family to a U.S. publication, which it did not name, and that the proceeds would go to charity.

"I've never known a set of pictures to be worth this amount of money," said Lyons, the owner of Big Pictures. He estimated that the twins' official photos will be worth between $15 million and $20 million.

The only other photos that "would possibly come that close is Britney Spears giving birth to an alien," he said.

Veteran London-based celebrity publicist Max Clifford estimated the first photos could fetch 10 million pounds _ roughly euro12 million or $20 million, "which would make it the biggest baby deal ever."

"These kind of pictures sell lots of magazines," he said. "It's a 10-million-pound ($20 million) gamble as to whether the ends justify the means. But obviously it's a very calculated risk because whoever lands the photos will have a lot of experience with the popularity of mum and dad."

Paparazzi have been following the couple through southern France since the Cannes film festival in May, snapping shots of the family on an outing to Eze beach and sticking close as they set up household in Correns, 60 miles from Nice. But so far the couple has evaded the paparazzi when it counted, arriving undetected at the Lenval clinic two weeks before the birth.

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Associated Press Writers John Leicester in Paris and Emily Ristow in London contributed to this report