'Gossip Girl' Shocker! You'll Never Guess Who Were Considered to Play Serena and Blair

The CW

It's hard to imagine anyone else but Blake Lively and Leighton Meester portraying Serena van der Woodsen and Blair Waldorf, but they weren't the first choices to fill the beloved Gossip Girl leading roles.

Casting director David Rapaport revealed that The CW initially wanted Rumer Willis to play Serena and Ashley Olsen to portray Blair.

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"I love Rumer, she's grown into quite an amazing actress and person," Rapaport told BuzzFeed. "But that, to me, was based on protecting the investment of a television show where creatively, these lesser-known girls really captured the essence of the show and carried it for six years."

He said Lively was always his pick to play Serena. "I had seen her in Accepted and at that time, there were no Lena Dunhams or Zooey Deschanels," he explained. "It was all about beauty and glamour, but being approachable and Blake was the ultimate It Girl."

As for Meester, Rapaport admitted that she "came off colder" than her co-star when she auditioned. That's why he thought she could pull off the part of Blair. "Leighton wasn’t a b**ch when she came in, but she wasn’t overly nice or overly generous," he recalled. "She was professional and she did the job and played the role well, and what I liked about her is that she owned who she was. She wasn’t going to kiss everyone’s a** and that was very Blair."

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While it was clear the girls were right for the roles, Rapaport says getting them hired had a lot to do with changing up their hair. Given Lively's long locks, execs weren't convinced that she could pull off the role of a rich New Yorker.

"So we did another screen test with Blake and all we did was straighten her hair to make her look a little more sophisticated, so to speak," Rapaport admitted. "What’s ironic is, in the pilot, she ends up having the wavy hair."

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Turns out, the hair was pretty important for Meester too.

"From there on out, so much of the casting on Gossip Girl became about the hair because Leighton Meester is naturally blonde and the way we got her the job was we dyed her hair," he added. "Ultimately they were the best actors for it and brought something really special to their roles."

WATCH: Chace Crawford Talks Life After Gossip Girl and Reuniting With Ed Westwick!

Gossip Girl
went off the air in 2012 after a six-year run, and looking back, Rapaport has no regrets about casting these leading ladies. "I feel like you go back and think, 'There is nobody else that could have played these characters,'" he said.

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The actresses' formerco-stars, Chace Crawford and Ed Westwick, now have new shows on ABC, Blood and Oil and Wicked City. ET caught up with Crawford, who was thrilled to be reunited with his Gossip Girl buddy.