Question: What year did the acress who portrayed Lady Prudence Shackleton on Downton Abbey join the board of the Mind the Gap Theatre?

Context articles: Joanne Froggatt
Mind the Gap Theatre
Zoe Boyle
List of Downton Abbey episodes
Harriet Walter
Michelle Dockery
Joan Benham
Shackleton (TV serial)
Personnel of the Shackleton–Rowett Expedition
Equality (Titles) Bill

Joanne Froggatt (born 23 August 1980) is an English actress of stage, television, and film.
 From 2010, she played lady's maid Anna Bates in all six seasons of the period drama "Downton Abbey".
 For this role, she received three Primetime Emmy Award nominations for Outstanding Supporting Actress in a Drama Series and won the Golden Globe Award for Best Supporting Actress on Television in 2014.
The brainchild of Paula D'Alessandris, Mind The Gap (MTG) Theatre Company was conceived in 1998 to import edgy British productions, readings and workshops to New York audiences and, in return, export some of America's unknown theatrical talent to the United Kingdom.
 Featuring An Anglo-American repertory company of actors and writers, the New York City-based company maintains active ties to an assortment of British theatre agencies and has a literary staff that reads hundreds of new scripts each year.
 In 2001, Dame Helen Mirren and Dame Judi Dench joined MTG’s Board of Advisors.
 In 2013 Dame Harriet Walter joined the board.
Zoe Boyle is an English actress known for her role as Lavinia Swire on the series "Downton Abbey" and Trinity Ashby on "Sons of Anarchy".
"Downton Abbey" is a British period drama television series created by Julian Fellowes and co-produced by Carnival Films and Masterpiece.
 It first aired on ITV in the United Kingdom on 26 September 2010, and on PBS in the United States on 9 January 2011, as part of the "Masterpiece Classic" anthology.
 Six series have been made, the sixth airing in the autumn of 2015 in the UK and Ireland, and in January 2016 in the United States.
 On 26 March 2015, the sixth series was confirmed to be the final series, with the final episode airing in the UK on 25 December 2015 on ITV.
 During the course of the programme, episodes of "Downton Abbey " aired over series.
Dame Harriet Mary Walter, {'1': ", '2': ", '3': ", '4': "} (born 24 September 1950) is an English stage and screen actress.
 Her film appearances include "Sense and Sensibility" (1995), "The Governess" (1998), "Villa des Roses" (2002), "Atonement" (2007) and "Man Up" (2015).
 On television she starred opposite John Lithgow as Clementine Churchill in "The Crown" (2016), Natalie Chandler in the ITV drama series "" (2009–14), and as Lady Prudence Shackleton in four episodes of "Downton Abbey" (2013–15).
 She was appointed Dame Commander of the Order of the British Empire (DBE) in 2011 for services to drama.
Michelle Suzanne Dockery (born 15 December 1981) is an English actress and singer.
 She is most widely known for her performance as Lady Mary Crawley in the ITV (UK) and PBS (U.S.) television period drama series "Downton Abbey" (2010–15), for which she was nominated for three consecutive Emmy Awards in the category for Outstanding Lead Actress In Drama Series, and a Golden Globe Award nomination.
 She made her professional stage debut in "His Dark Materials" in 2004.
 For her role as Eliza Doolittle in the 2007 London revival of "Pygmalion", she was nominated for the Evening Standard Award.
Joan Benham (17 May 1918 – 13 June 1981) was an English actress best known for her portrayal of Lady Prudence Fairfax in the ITV period drama series "Upstairs, Downstairs".
 She was born in London and was the first cousin of Hollywood actress Olive Sturgess.
Shackleton is a 2001 British television film written and directed by Charles Sturridge and starring Kenneth Branagh as explorer Sir Ernest Shackleton.
 The film tells the true story of Shackleton's 1914 Antarctic expedition on the ship "Endurance".
 The cast includes Kevin McNally, Lorcan Cranitch, Embeth Davidtz, Danny Webb, Matt Day and Phoebe Nicholls (also the director's wife) as Lady Shackleton.
 It was filmed in the UK, Iceland and Greenland.
 The film used first-hand accounts by the men on the expedition to retell the story.
 Shackleton biographer Roland Huntford was a production advisor.
The Shackleton–Rowett Expedition, 1921–22, was the last Antarctic expedition led by Sir Ernest Shackleton.
 Proposed as an ambitious two-year programme of Antarctic exploration it was curtailed by the death of Shackleton and the inadequacies of the expedition's ship, "Quest".
 Under the command of Frank Wild several attempts were made to break through the Antarctic pack ice, but the expedition was never able to proceed further than longitude 20°E. On the crew's return to Cape Town to refit in preparation for the second term they were ordered home.
 The crew of the "Quest" comprised 24 members in all, but only 19 were on board for the start of the Antarctic portion (Hussey accompanied Shackleton's body when it was put on board a ship for England, and Eriksen, Mooney and Bee-Mason had left before the ship reached South Georgia).
 Gerald Lysaght, a yachtsman, accompanied the crew from Plymouth to Cape Verde.
The Equality (Titles) Bill, known colloquially as the "Downton Law" and "Downton Abbey Law", was a Bill of the Parliament of the United Kingdom that would end a measure of gender discrimination and allow for equal succession of female heirs to hereditary titles and peerages.
 The primogeniture legislation, in conjunction with the Succession to the Crown Act 2013, would align hereditary titles in accordance with the 1975 Sex Discrimination Act.