ENTERTAINMENT WEEKLY – The first time Saoirse Ronan and Margot Robbie saw each other on the set of Mary Queen of Scots, they ended up on the floor, crying in each other’s arms.

It was Ronan’s first day as the titular royal, and Robbie’s last as her cousin and rival, Elizabeth I. The two actresses had been kept apart throughout rehearsals and production until then; Robbie filmed in England, Ronan would be shooting in Scotland, and at their request, they never crossed paths in character prior to their sole scene together. “We really, really didn’t want to see each other,” Ronan says. “I love Margot and wanted to hang out, but we wanted [the meeting] to be this special thing.”

Yet, when the time finally came for them to perform the queens’ confrontation, well… “We were blubbering like idiots,” Ronan tells EW. “We just held each other for ages, we wouldn’t let go. We were like” — she lowers her voice to demonstrate their sobbing — “‘Huohooouuughh.’” She laughs. “I’ve never experienced anything like that.”

Then again, her real-life counterpart never did either. Historians believe the Queen of Scots and the Virgin Queen never met, but theater director-turned-first-time film helmer Josie Rourke was inspired by the 19th-century Friedrich Schiller play Mary Stuart, in which Mary and Elizabeth talk face-to-face on stage. “The whole conception of the film for me was around that meeting,” Rourke says of the historical drama. “We really wanted to have our version of that famous scene, with these two women looking at each other and being confronted with their choices — their personal choices, their political choices. It’s a moment that’s deeply personal.”

And deeply emotional. The waterworks on set may have been caused by the high stakes (and excitement) of capturing the only time the stars share the screen, but Robbie thinks those tears also stemmed from how much they’d delved into the tragedy of their characters’ histories. (For Elizabeth: Her mother was beheaded by her father. For Mary: She lost her husband before she turned 18. And both were often targeted by religious groups, political conspirators, and marriage treaties.) “I had underestimated how difficult their lives were, and how much pain was wrapped up in this power,” Robbie says. “I think it just meant more.”