Saoirse Ronan and Margot Robbie didn't rehearse together on purpose for 'Mary, Queen of Scots'

Saoirse Ronan was so excited to star in "Mary, Queen of Scots" that she signed on for the role six years ago!

The Oscar-nominated actress stopped by "Good Morning America" on Tuesday to talk about her buzzy new film, also starring Margot Robbie as Queen Elizabeth I.

Ronan said playing Mary Stuart, the former Queen of Scotland in the mid-1500s, was such a "massive" undertaking. She signed on in 2012 and it took that long "to get the right people to come on board."

"Luckily, it's one of those roles you just sort of grow into," the 24-year-old actress said.

One of those "right" people was fellow Oscar nominee, Robbie, who plays her character's cousin and as history shows, the woman who would later have Mary beheaded.

The two actresses are great friends off-set but the "Lady Bird" star revealed Tuesday that they decided to "barely" see each other during filming.

"We stayed apart," she said. "We thought it would be this kind of really cool experiment to try."

The movie builds up to one emotional reunion between the two women and Ronan said she had now idea how Robbie was going to act in the scene.

"When we finally see each other for first time [in the film], it was really the first time [we saw each other on set]," she added.

Ronan said after the first take, both she and Robbie were crying and "wouldn't let each other go."

"Mary, Queen of Scots" is out now in select theaters.