Grantchester's Robson Green teases major cameo in upcoming series 8 - and fans think they've worked out who it is!

Grantchester star Robson Green has teased a major cameo in the upcoming eighth season of the popular ITV detective drama - and fans think they have guessed who it may be!

MORE: Grantchester season eight: Everything we know so far - cast, plot, more

Taking to Instagram, the actor shared a photo which showed him and his co-star Tom Brittney on the set of series eight, sitting on a bench next to another actor who has been cropped out of the snap.

WATCH: Grantchester stars share hilarious behind-the-scenes skit

In the caption, Robson wrote: "Chillin’ with me Vicar that is @tombrittney alongside our very special guest for this series who just happens to be one of the nicest guys on the planet and one of my closest friends! All will be revealed in the new series! @itv @masterpiecepbs @pbs #grantchester."

Fans rushed to the comments section to share their guesses, with many believing the mystery guest star to be either Mark Benton, known for his roles on Waterloo Road and Shakespeare & Hathaway: Private Investigators, or Game of Thrones star Jerome Flynn.

One person wrote: "Can’t wait!! Great picture…. Is it Jerome Flynn! You should sing 'I believe' in the local," while another agreed, adding: "Would love to see Jerome Flynn appear on Grantchester at some point please."

MORE: Grantchester teases despair for newlywed Will in upcoming season eight

MORE: Meet the Grantchester cast's real-life partners

Another fan commented: "Mark Benton maybe," while another wrote: "Must be Mark Benton!"


Robson teased a major guest star for season eight

Robson and Mark starred together in ITV's comedy-drama Northern Lights back in 2006 as best friends Colin and Howard.

Fans suspect that Jerome may be joining Robson in season eight as the pair performed together as the music duo, Robson & Jerome, in the 1990s. The singers rose to prominence thanks to the ITV war drama Soldier Soldier, in which they both starred, after an episode saw the pair perform a rendition of Unchained Melody by The Righteous Brothers, triggering a huge response from viewers.

Unfortunately, fans may have to wait a while to find out who the special guest star is as the drama is set to return some time next year.

Viewers can expect to see Geordie and Will face tough times in the new series as the synopsis reads: "Will is the happiest he's ever been but his world will be rocked by a terrible accident. He's always preached the word of a compassionate God – but how can he now, when his despair leads him on a dangerous downward spiral?


The series returns next year

"Geordie has found a new contentment in his relationship with Cathy, but when they are both confronted with shocking announcements at work their happiness is threatened. As Mrs C, Leonard, Jack and Daniel rally around, both Will and Geordie find themselves in unfamiliar, emotional waters and murder is always around the corner."

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