Once Upon a Time in Hollywood takes place in Los Angeles in 1969. The movie follows an aging actor (DiCaprio) and his stunt double (Pitt), who encounter real-life Hollywood figures, including Tate. Tate, a model and actress, was 26 and pregnant when she was killed by members of the Manson Family in August 1969.
"Whenever I heard her name, I really only thought about her death. I was never really exposed to the parts of her life when she was alive," Robbie said.
Tate's sister Debra Tate gave her blessing to the film and provided jewelry of Tate's for Robbie to wear.
"It was kind of sometimes very sad to be that closely connected with real-life Sharon," Robbie said. "It kind of hit you at moments and suddenly the tragedy of it all would kind of hit you and you would be tremendously sad. Other times, it made me feel so happy. But yes, there were moments where it was very sad."
"I find it much easier to go dark and angry. With Tonya, I wanted to go really heavy, almost like she had weights on her feet," she said. "This time I was trying to do the reverse."
Once Upon a Time in Hollywood opens in theaters July 26. The film released a trailer in May featuring Pitt and DiCaprio.