ET was on the red carpet Thursday night with Drew Barrymore, and Jessica Lange at the Los Angeles premiere of the new HBO film 'Grey Gardens,' and Barrymore reveals the truth about her relationship with Justin Long.

In the film Lange and Barrymore play "Big Edie" Bouvier Beale, and "Little Edie" Bouvier Beale an eccentric mother daughter pair who were relatives of Jacqueline Bouvier Kennedy Onassis, played by Jeanne Tripplehorn.

"Our biggest goal was to disappear into the characters," Barrymore tells ET. "All we wanted was to not be seen and just have these two women come to the forefront. Their love stories, their struggles, their endearing heart-breakingly exceedingly comical, amazing journey. All I can say is that I'm the luckiest person that I got the opportunity to play a woman who is so full of so many extraordinary colors. I've never read seen or known anyone like her."

The film which debuts April 18 on HBO is based on a documentary made in 1975 by Albert and David Maysles, about the two Beale women who chose to live in isolation in East Hampton until Jackie-O helped them to save their house and clean up their lives.

Watch the video to find out how the actors went to extremes to get into their characters, and Barrymore dishes on the status of her relationship with guy pal Justin Long.