Taylor Swift's actor boyfriend Joe Alwyn to play Margot Robbie's lover

Taylor Swift's actor boyfriend Joe Alwyn has been cast as Margot Robbie's lover in the upcoming Mary Queen Of Scots movie.

The 26-year-old star will appear alongside Margot, who is playing Queen Elizabeth I in the movie, as Elizabeth's counselor and lover Dudley.

Irish actress Saoirse Ronan is also on the cast list, playing the titular Mary Stuart. According to The Hollywood Reporter, the film "centers on Mary, who, as a child, was taken to France and betrothed to the French King’s eldest son Francis. But her marriage is short lived when Francis dies a year after being crowned and Mary returns to Scotland in an attempt to regain favor with her cousin, Queen Elizabeth".

The gig is the biggest in Joe's career to date, with the actor only having starred in three movies so far, including Billy Lynn's Long Halftime Walk, his first on-screen role in 2016. He also appeared in The Sense of an Ending earlier this year (17), and will next be seen in The Favorite, alongside Rachel Weisz and Emma Stone.

Some may speculate that Joe's relationship with Taylor may have something to do with him landing the new Mary Queen of Scots role, considering he was a little-known actor prior to the start of his relationship with the Shake It off singer earlier this year.

However, Taylor is doing her best to keep this romance under the radar, considering her fling with Tom Hiddleston played out so publicly - from the beginning to the bitter end.

"She got buried in media being on top of her life during the last relationship, so she tried everything in her power to not have that happen again," an insider told E! News recently. "She worked very closely with her security team and management to make sure her life going forward was private. All of that madness really affected her.

"She is very protected and is trying to peddle slow with this."