Downton Abbey is soon to return for its sixth and final series - and star Michelle Dockery has warned fans they are in for a shock.

The actress, who plays Lady Mary in the hit period drama, told Harper’s Bazaar her character gets her “bite” back as the show comes to a close.

Dockery, 33, also shared her excitement at returning to the London stage this year, saying the end of Downton felt more like “the beginning of something than the end”.

The final series starts on ITV1 on September 20. Dockery said: “I’ve got such a great story - Lady Mary’s bite kind of comes back again. When I read the scripts, they really surprised me.

“How Mary is and what happens is quite shocking. There are always twists and turns in the plot — there are every year — but this year particularly, there’s a bit of a U-turn that happens with Mary, and it’s amazing.

“It is another kind of challenge and another really interesting series for me. Just when you think Julian [Fellowes, Downton creator] has exhausted the possibilities of a character, he manages to throw in something else that pulls the rug from under you.

“On a show like this, when you’re playing a character — the same character — all the time, you want to still feel like you’re being challenged.”

Dockery, who grew up in Romford, has played Lady Mary for so long that some fans assume she is the same in real-life.

She said: “I was once asked in America if I had a housemaid and someone who cooked for me, which I found hilarious.” Her next challenge will be starring with Dominic West in Les Liaisons Dangereuses at the Donmar Warehouse.

BAFTA celebrates Downton Abbey 5 show all BAFTA celebrates Downton Abbey 1/5 Belle of the ball: Lily James wears a white dress an towering stilettos as she hits the red carpet (Tim P. Whitby/Getty Images) 2/5 Striking: Daisy Lewis makes sure she stands out in a magenta gown (Tim P. Whitby/Getty Images) 3/5 Bidding farewell: Julian Fellowes and Emma Joy Kitchen pose for photos ahead of the event (Tim P. Whitby/Getty Images) 4/5 In support: Hugh Bonneville who plays Lord Grantham with his wife Lulu Williams. (Tim P. Whitby/Getty Images) 5/5 She's back: Myanna Buring looks stunning in a lace navy dress (Tim P. Whitby/Getty Images) 1/5 Belle of the ball: Lily James wears a white dress an towering stilettos as she hits the red carpet (Tim P. Whitby/Getty Images) 2/5 Striking: Daisy Lewis makes sure she stands out in a magenta gown (Tim P. Whitby/Getty Images) 3/5 Bidding farewell: Julian Fellowes and Emma Joy Kitchen pose for photos ahead of the event (Tim P. Whitby/Getty Images) 4/5 In support: Hugh Bonneville who plays Lord Grantham with his wife Lulu Williams. (Tim P. Whitby/Getty Images) 5/5 She's back: Myanna Buring looks stunning in a lace navy dress (Tim P. Whitby/Getty Images)

The actress has previously appeared at the Old Vic, receiving a nomination at the 2008 Evening Standard Theatre Awards for Pygmalion, and the National Theatre Lyttelton.

Of her Donmar role she said: “Of course, it’s a period drama — but wanting to take it on has nothing to do with that. I’m in love with the story and the character. I’ve always had in mind that I would finish Downton and go on to a play, because I want to go back to where I started.

“In fact, I’m longing for it. There’s so much more I want to do, and I feel like Downton Abbey has given me the opportunity for that. I don’t just mean in acting; I mean in my life. It feels like more of the beginning of something rather than the end.”

Her next television role, in US series Good Behavior, will be a stark contrast to Lady Mary — she plays a con artist, Letty, recently let out of jail. “It’s about a woman tackling her demons; trying to escape her dark past,” she said.

“I’m excited to be playing a character that is so emotionally raw. Downton is all about calmly dealing with situations without getting emotional about them. Letty’s an animal.”