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Katherine Schwarzenegger has her brother Patrick Schwarzenegger's back.

She's all for his romance with Miley Cyrus.

"I approve of whatever makes my brother happy," Katherine said about the relationship at last night's premiere of Dior and I.

Is her brother happy right now?

"He's a 21-year-old college kid, how could he not be?" Katherine said.

Maria Shriver and Arnold Schwarzenegger's oldest child certainly was happy last night.

She had never work Dior until she slipped into one of their dresses last night.

"It's my first time!" Katherine said. "I lost my Dior virginity."

Katherine Schwarzenegger

Michael Tran/FilmMagic

She gushed over the hot pink mini-dress. "I feel really lucky," she said. "It's so comfortable. It's a really nice fabric."

Katherine also revealed that the white Prada heels she was wearing were her most recent fashion splurge.

"I have a whole wall in my apartment of shoes," Katherine said. "It's not normal but it's a good addiction to have."

Dior and I follows Belgian designer Raf Simons as he creates his first haute couture collection shortly after being named creative director of the legendary French fashion house in April 2012. Directed by Frédéric Tcheng, the film includes appearance by Oscar winners Jennifer Lawrence and Marion Cotillard, Anna Wintour and Sharon Stone.

Tcheng said the idea of the documentary began percolating after reports suggested Simons was the first choice to replace Bill Gaytten at Dior.

"Raf has such a unique point of view of fashion. He's sort of an outsider," Tcheng said. "For him to arrive at such a big house as Dior was going to be promising in terms of drama."

Also at last night's premiere at LACMA were Jaime King, Britt Robertson, Teresa Palmer, Ahna O'Reilly, Isabel Lucas, Younger star Nico Tortorella and designer Rachel Roy.

For more from the Dior and I premiere, watch E! News tonight at 7 p.m. or 11 p.m.