Patricia Hodge will play Bertie Pelham's mother in the 'Downton Abbey' Christmas special.

The cast of 'Dowtnon Abbey'

The cast of 'Dowtnon Abbey'

ITV and Carnival Films have today (13.11.15) announced details of the final ever episode of the much-loved period drama and revealed it will see the Crawley family celebrate New Year's Eve at the home of Lady Edith's (Laura Carmichael) fiancee Bertie, the new Marquess of Hexham (Harry Hadden-Paton).

'Miranda' actress Patricia is set to play Bertie's demanding mother while Lily James and Matt Barber are to return as Lady Rose and Atticus Aldridge alongside Peter Egan as Rose's father Shrimpie.

The series six finale saw Lady Mary (Michelle Dockery) ruin her sister Edith's engagement to Bertie by telling him about her illegitimate daughter Marigold, and in the Christmas special she endeavours to build bridges while the secret continues to pose a threat.

Meanwhile, Mary's new husband Henry Talbot (Matthew Goode) struggles to find his place at 'Downton' and butler Mr. Carson (Jim Carter) faces some personal challenges which prove even his is not invulnerable to change.

Producers have teased that the last ever episode will offer all the love and loss, happiness and heartbreak that fans of the show have come to expect, as the family and servants prepare to bring in the year 1926 as they celebrate an unforgettable New Year's Eve together.

Filming of the upcoming special took place over a week at Alnwick Castle in Northumberland - which doubled as Bertie's Brancaster home - and at the iconic Ritz hotel in London.

In addition to new and returning cast members, the episode will also feature regular stars including Maggie Smith, Hugh Bonneville, Elizabeth McGovern, Phyllis Logan and Joanne Froggatt among others.

'Downton Abbey' returns to ITV on Christmas day (25.11.15).