The relationship between Lady Mary and Lady Edith has been tense since the beginning of ‘Downton Abbey’ and not a lot will change between the siblings when season six premieres.

Actress Michelle Dockery, who plays the elder sister, admitted that while the two will always stay in each other's lives, the pressure between them will intensify as the series brings on its concluding episodes this autumn.

The widely-acclaimed period drama will return to ITV for its final installment on January and fans will get to see Dockery reprise her role as the calm and unyielding Lady Mary, who reveals that she will take over as estate manager of the family's home.

Aside from having a new love interest, season six will follow the relationship between Mary and Edith, portrayed by Laura Carmichael.

Dropping hints of the upcoming storyline, the 33-year-old English actress opened up about the new installment to a press conference in London.

"The relationship between Edith and Mary is still very town and country. It's lovely that contrast, their lives run very parallel to one another in the first half of the series,” Dockery said.

She further explained that the tension heats up between the Crawley sisters, with the elder sibling becoming more spiteful as she looks at Edith’s experiences.

“There's more of a pressure cooker between them now because there's still this rivalry and Mary's a little envious of Edith's life in London. Edith's living in a house which Mary is now running,” Dockery added.

The sisters have already experienced much heartbreak over the past five seasons as Mary's husband Matthew Crawley died after the birth of their son while Edith was left at the wedding altar by Sir Anthony Strallan.

In the middle of their difficulties and despite their edgy relationships, Dockery stated that the sisters will always have each other’s backs.

“Men have come and gone from their lives but actually the two of them, they can't be without each other. They're sisters and they've experienced so much together and in spite of their differences they're family,” the actress explained.

Season six will also see Edith taking on the position as editor-in-chief of Sketch newspaper as she lives a new life in London while Mary becomes a committed businesswoman who will take charge of the management of ‘Downton Abbey’ and its finances.

‘Downton Abbey’ season six is set to premiere on Jan. 3, 2016. Its official trailer can be viewed below.