But Isaac Hempstead Wright, who plays Bran Stark on the HBO fantasy drama, couldn't resist spilling the beans to his mother, Helen.
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The English actor, who has starred on Game of Thrones since he was 10 years old, made the revelation during an interview with The Project on Monday.
Speaking to comedian Peter Helliar, the 20-year-old heartthrob recalled telling his mother what happens in the last episode.
'I was calling her on the phone, like, "I know how it ends," and she was like, "Tell me!" and I said, "I can't, the phone might be tapped!"' he said.
'I actually told her while I was in the car, and my dad was driving and he really didn't want to know, and I was trying to whisper.
'He was like, "La-la-la-la! I'm going to crash the car! Stop!"'
Isaac added that the final season had been the most fun to film because it was the first time the entire cast had been able to act alongside one another.
'This season more than ever, there's been such a sense of camaraderie, because for once, we all feel like we're part of the same story,' he explained.
'So this season, where it's all just one big plot, it's been so much fun getting to act with people I never ever thought I'd get to act against. Like, getting to act with Emilia Clarke as Daenerys, that's a character I've loved watching in the show.'
But given the bloody nature of the fantasy series, Isaac said the cast was constantly on edge, worried their characters would be killed off.
He admitted that the first thing he would do whenever he received a new script was flick through to check that Bran Stark survives.
Isaac also revealed the actors whose characters were about to be killed off received a 'call of death' from the producers to give them a heads-up.
