His Dark Materials season 3 casts Fleabag and Sherlock stars

His Dark Materials spoilers follow.

His Dark Materials has announced two additional cast members for its upcoming third series: Sian Clifford and Jonathan Aris.

Clifford rose to fame playing Claire in Fleabag for which she won a BAFTA and received a Primetime Emmy nomination. Last year, she also starred in ITV limited series Quiz.

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Aris, meanwhile, has previously starred in BBC's Sherlock alongside Benedict Cumberbatch and more recently appeared as the angelic quartermaster in Amazon Prime Video's Good Omens.

london, england november 04 jonathan aris attends the world premiere of the end of the fing world at genesis cinema on november 4, 2019 in london, england photo by david m benettdave benettwireimage

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Clifford and Aris will play Agent Salmakia and Commander Roke respectively, characters described as 'Gallivespian Spies' in the Philip Pullman book series, Deadline reports.

The new cast members also have a connection to a season 2 star, as both Clifford and Aris have previously worked with John Parry actor Andrew Scott, who starred with Clifford in Fleabag and Aris in Sherlock.

Sadly, it's unlikely we'll see an on-screen reunion as Scott's character in His Dark Materials met his demise in the second season.

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The majority of the main cast are returning for the third and final season, including Dafne Keen as Lyra, Amir Wilson as Will, Ruth Wilson as Mrs Coulter, and James McAvoy as Lord Asriel.

HBO also recently announced other new additions to the cast, including Adewale Akinnuoye-Agbaje (Suicide Squad) as Commander Ogunwe, and Kobna Holdbrook-Smith, Simon Harrison and Chipo Chung as rebel angels Balthamos, Baruch, and Xaphania respectively.

The series was officially renewed back in December and kicked off production on the third series in May.

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This final season is based on Philip Pullman's The Amber Spyglass, which will see Lyra and Will travel through various different worlds in order to reunite.

James McAvoy previously teased what's to come in the next season, saying: "It's war. At the end of the second season we sort of declare war on the Kingdom of Heaven, so yeah it gets pretty down and dirty, and there's gonna be a lot of fisticuffs and a lot of explosions and all that stuff.

"But at its heart it's about a wee girl and a wee boy... and not the adults with the egos."

His Dark Materials airs on BBC One in the UK and HBO in the US.