'Knightfall' 's Tom Cullen Says He's Ready for Girlfriend Tatiana Maslany to 'Put a Ring on It'

Tom Cullen scored a save-the-date for close friend Kit Harington‘s wedding to Game of Thrones costar Rose Leslie — and he admits seeing his mate from drama school back in London propose “absolutely” has him thinking about popping to question to longtime girlfriend Tatiana Maslany.

“I’m just waiting for her to put a ring on it,” he quips of the Emmy-winning Orphan Black actress in this week’s issue of PEOPLE, on stands Friday. “I mean, I don’t know what she’s waiting for.”

Cullen and Maslany, both 32, met and fell in love filming a miniseries in 2011 and have been together ever since. (He recently relocated to Los Angeles to be with her!) They costarred in the 2016 indie The Other Half, and he’s directing her in an upcoming film shot in his native Wales.

“I like working with her because she’s so amazing, and I just love to work with people who terrify me, because then they’re so good,” he says. “And she is the most terrifying actor I’ve ever worked with, because she’s the best actor I’ve ever worked with.”

As for Jon Snow‘s nuptials, we know nothing.

“I’ve been invited, but I can’t tell you when it is, I’m afraid. I’m so sorry,” he says with a laugh.

• For more on Tom Cullen, pick up this week’s issue of PEOPLE, on stands Friday

Watch Cullen in the epic new drama Knightfall, airing Wednesdays at 10 p.m. ET on the History Channel.