Joe Jonas had to sign an non-disclosure agreement (NDA) before he could visit his fiancée Sophie Turner on the set of Game of Thrones.

The 23-year-old actress plays Sansa Stark in the HBO fantasy drama which is set to come to an end this month when the eighth and final season airs, and she's said her husband-to-be Joe Jonas, 29, had to sign a legal document preventing him from talking about the show's highly anticipated ending when he visited her on set.

Sophie said: "He was on set for most of [filming the final season], so he kind of figured [the ending] out. He had to sign an NDA."

And the blonde beauty also revealed the Jonas Brothers singer had to have the camera lens on his phone covered up, in order to prevent him from taking sneaky pictures of the filming.

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She added: "He had to have full photo approval on set, his camera was covered up, everything."

But despite the lengths bosses went to to prevent Joe from talking, Sophie doesn't think he'd be able to keep it to himself.

Speaking on Good Morning America, she joked: "You can give him a call, he'll probably tell you everything."

Meanwhile, Sophie recently claimed she'd told the 'Sucker' hitmaker how the show ends, and said he was "mad" at her for spoiling the dramatic plot twists.

She said: "I've just told Joe [Jonas]. But he's so mad at me - he loves the show! Well, I have to tell someone, otherwise I'll burst."

And she's not the only person to have ruined the show for their loved ones, as her on-screen brother Kit Harington, who plays Jon Snow, recently revealed his wife Rose Leslie - who previously appeared on the show as his on-screen lover Ygritte, before departing in season four - refused to speak to him for "three days" after he told her key plot spoilers.

Kit said: "I told my wife last year how it ended, and she wouldn't talk to me for about three days. And she'd asked!"