The cast of Gossip Girl would have looked completely different if it weren't for The CW's casting director, David Rapaport. Network executives were initially considering Ashley Olsen and Rumer Willis to star in the show. Rapapaort explained why he stuck with his gut in casting Blake Lively and Leighton Meester to dominate the Upper East Side in New York City, unveiling secrets from behind the scenes. Lively's audition tape also surfaced, proving why she was meant for the role.

The CW took fans through six seasons filled with tumultuous drama, enviable wardrobes, random hookups, and an extremely hot cast. It's hard to imagine the teen-drama series without the leading female frenemies, Serena van der Woodsen (Lively) and Blair Waldorf (Meester). Well, according to a recent interview with BuzzFeed News, the Dancing With the Stars season 20 winner was pitched for the role of Serena before Lively.

"I think the network initially pitched us Ashley Olsen and Rumer Willis for Blair and Serena," Rapaport said to BuzzFeed News. "I love Rumer, she's grown into quite an amazing actress and person, 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."

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Despite his love and appreciation for Bruce Willis' eldest daughter, the 37-year-old casting director had his eye on another budding actress (Lively). Rapaport admitted when he looks for an actor or actress to cast in a role, he tries to find someone who the audience will ultimately fall in love with, the same way he falls in love with the characters when choosing them.

When it came down to the final picks for the role of Serena, Rapaport and the rest of the casting crew narrowed it down to Lively, Arrow's Katie Cassidy, and a girl who modeled on the Gossip Girl book covers. He revealed The Age of Adaline actress was the front-runner out of the three girls and why he was so adamant about her starring in the series.

"Blake Lively was literally the only person I could think of for Serena. I had seen her in Accepted, and at that time there were no Lena Dunhams or Zooey Deschanels - it was all about beauty and glamour, but being approachable and Blake was the ultimate It Girl," Rapaport told Buzzfeed, "I was terrified we wouldn't get her or they wouldn't like her because, honestly, the show lived and died on her and I had absolutely no other ideas."

Rapaport, who's also done casting for The Flash and The CW's 90210, had a hunch about who Meester should play on the show based off her personal demeanor. He knew the way she carried herself was just another way to act out the part, but that also made it easier for him to choose between other actresses who were too nice or flirting to get his attention. Although a natural blonde, Meester's hair was dyed brown to officially complete her transformation into Blair.

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Anyone familiar with Blair's character might find it extremely hard to picture Olsen as a mean girl. Rapaport says he doesn't believe anyone else could play those roles and carry the seasons like Lively and Meester did.

"I'm not looking for you to love me" he said to Buzzfeed, "I'm looking for your personality. I'm looking for your uniqueness, so to speak. And Leighton wasn't a bitch when she came in, but she wasn't overly nice or overly generous. 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 ass and that was very Blair."

There are no hard feelings between any of the actresses, because each woman has found success in her own right. Olsen, 29, runs a multimillion dollar business with her twin sister Mary-Kate, while Willis, 27, went on to headline Broadway's Chicago. Lively, 28, and husband Ryan Reynolds have a daughter named James together, while Meester, 29, and husband Adam Brody welcomed daughter Arlo in August.

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