Warning: This article contains major spoilers about The Blacklist season 5 finale.

The Blacklist delivered an almighty twist (and confirmed a long-running fan theory in the process) as Megan Boone's character Liz made a shocking discovery in the fifth season finale.

In a twisty end to the season, Liz finally figured out that the bones belonged to the real Raymond Reddington – which means that James Spader's character who has claimed to be Red all this time is an impostor.

Whaaat.

NBC Universal

"This is something that we've talked about from the inception of the show," show boss Jon Bokenkamp told Entertainment Weekly. "It is part of the underlying mythology that we've slowly been unraveling.

"I think there are a number of episodes that we can go back and sort of map and chart how we got here. Hopefully that is proof of concept to the audience that this is not something we're just winging, and that we're on a very specific path, and this is a well-earned reveal."

Bokenkamp confirmed that Spader has known for a long time that he was playing an imposter, but the rest of the cast were kept in the dark.

Will Hart/NBC/NBCU Photo Bank via Getty Images

And although the series creator refused to reveal who Spader's character really is, saying that it will play a big part in season six, he teased that the dynamic between the impostor and Liz will drastically change.

"He does not know that she knows," Bokenkamp explained. "I think that piece of information is really compelling.

"This blows up everything... Very rarely does anyone know something that Reddington doesn't know, right? He's always ahead of the curve. He's a very cunning and smart, brilliant mastermind criminal, and yet he didn't see this one coming. So I think that is a real power shift and something that we haven't explored in past seasons."

The Blacklist airs on NBC in the US and on Sky1 in the UK.

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