Angelina Jolie and Brad Pitt "have proven once again that they are the leaders in original baby-naming, even by Hollywood standards," baby name expert Pamela Redmond Satran, coauthor of Cool Names and The Baby Name Bible, tells Usmagazine.com.

The actress, 33, gave birth to twins Knox Leon and Vivienne Marcheline at the Fondation Lenval hospital in Nice, France on Saturday.

(See 15 photos of her bump.)

"Vivienne is the French version of the ancient Latin name that means 'alive,'" Satran explains. A common English variation is Vivian, which was the name of Julia Roberts' character in Pretty Woman.

Except for Rosie O'Donnell's daughter Vivienne, the name "has not been on the fashion scope in the U.S.," Satran adds.

Jolie and Pitt's choice of Knox will boost its popularity among new moms, Satran predicts, "the same way they have with all their other children's names."

(See photos of Angelina and her children.)

Knox -- Pitt's grandfather's middle name -- also "matches" big brothers Maddox and Pax as a name that ends in X, Satran points out.

As for middle names, Marcheline was the name of Jolie's mother, who died of cancer last year, while Leon is Jolie's great-great grandfather's name.

(See photos of Angelina through the years.)

Satran gives Jolie and Pitt credit for their name choices.

"I applaud Brad and Angelina for being truly creative in a way that many other parents -- celebrities and the rest of us -- claim they want to be but aren't brave or individualistic enough to really achieve," she says. >>>>

Hard Knox for Jolie-Pitt boy, but Vivienne shines

Knox Leon's first report card wasn't great. Or maybe it's just that his twin sister, Vivienne Marcheline, ruined the curve.

When babies are born to celebrities, the burning question — after establishing that everyone's healthy, of course — is inevitably, "So what's the name?"

Blame it on Suri, Apple, Moses, Shiloh, Pilot Inspektor and Sunday Rose. Famous people just can't seem to help but hang interesting monikers on their kids.

The Associated Press asked a few baby-name experts — people who make their living consulting regular folks on christening their offspring — to break down celeb baby names as they happen and assign them a letter grade.

We start with the twins born to Angelina Jolie and Brad Pitt on Saturday in Nice, France. (Maybe you'd heard?)

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EXPERT: Whitney Walker, co-author with Eric Reyes of "The Perfect Baby Name" and consultant through ThePerfectBabyName.com.

SPECIALTY: Phonetics and rhythm — how names sound and flow together.

IMPRESSIONS: "Knox Leon has the short 'O' vowel sound in both names, so they match. ... Vivienne Marcheline is kind of a mouthful, but rhythmically it goes together because both names are French, with the accent on the last syllable.

"It seems they've got some kind of fixation with always having an 'X' in the boy's name. ... It used to be people named their kids with the same first letter; people frown on that now as a little too cliche. But she wants them to have something in common. And 'X' is unusual, it stands out.

"I'm sure she's going to call them Knox and Viv, and the 'V' and the 'X' kind of tie them together. ... She's going to say these names together a lot; you want them to sound good together, and not be too disjointed."

GRADE: Knox Leon: B-minus, Vivienne Marcheline: B-plus. >>>>