In May 2011, Queen Elizabeth II visited Ireland following an invitation from then president Mary McAleese.
Britain's Queen Elizabeth II (L) and Prince Philip,The Duke of Edinburgh visit the Guinness Storehouse Gravity Bar in Dublin, on the second day of the Queen's four-day visit to Ireland, on May 18, 2011. Queen Elizabeth II Wednesday visits an Irish stadium where British troops massacred 14 people, trying to heal old wounds in a historic step that would have been unthinkable for most of her reign. AFP PHOTO / Maxwells / POOL (Photo by Maxwells / POOL / AFP) (Photo by MAXWELLS/POOL/AFP via Getty Images)
CORK, IRELAND - MAY 20: Queen Elizabeth II meets Elizabeth Fitzpatrick of the Alternative Bread Company in the Old English Market on May 20, 2011 in Cork, Ireland. Queen Elizabeth II and Prince Philip, Duke of Edinburgh are on the final day of their historic four-day tour of the Republic of Ireland amid tight security, the first visit to Ireland by a British monarch since 1911. (Photo by Irish Government - Pool/Getty Images)
CORK, IRELAND - MAY 20: Protesters demonstrate against the state visit by Queen Elizabeth II as she travels to English Market on May 20, 2011 in Cork, Ireland. The Duke and Queen's visit to Ireland is the first by a monarch since 1911. An unprecedented security operation is taking place with much of the centre of Dublin turning into a car free zone. Republican dissident groups have made it clear they are intent on disrupting proceedings. (Photo by Oli Scarff/Getty Images)
CASHEL , IRELAND - MAY 20: Queen Elizabeth II is accompanied by Minister for Public Expenditure and Reform Brendan Howlin (R) and Dr Eugene Keane, Office of Public Works (Historic Properties Division) during a tour of St Patrick's Rock on May 20, 2011 in Cashel, Ireland. Queen Elizabeth II and Prince Philip, Duke of Edinburgh are on the final day of their historic four-day tour of the Republic of Ireland amid tight security, the first visit to Ireland by a British monarch since 1911. (Photo by Irish Government - Pool/Getty Images)
CORK, IRELAND - MAY 20: Queen Elizabeth II meets Angie Benhaffaf (R) with her one of her twin sons, Hassan, while visiting the Tyndall National Institute on May 20, 2011 in Cork, Ireland. Twins Hassan and Hussein were conjoined at birth and separated in an operation in the UK performed by surgeon Dr Edward Kiely from Cork. Queen Elizabeth II and Prince Philip, Duke of Edinburgh are on the final day of their historic four-day tour of the Republic of Ireland amid tight security, the first visit to Ireland by a British monarch since 1911. (Photo by Irish Government - Pool/Getty Images)
CORK, IRELAND - MAY 20: Queen Elizabeth II is accompanied by Taoiseach (Prime Minister) Enda Kenny as they inspect a guard of honour for the Queen and Duke's departure at Cork Airport on May 20, 2011 in Cork, Ireland. Queen Elizabeth II and Prince Philip, Duke of Edinburgh are on the final day of their historic four-day tour of the Republic of Ireland amid tight security, the first visit to Ireland by a British monarch since 1911. (Photo by Irish Government - Pool/Getty Images)
DUBLIN, IRELAND - MAY 17: Protesters demonstrate in the streets adjacent to the Garden on Remembrance where Queen Elizabeth II laid a wreath on May 17, 2011 in Dublin, Ireland. The Duke and Queen's visit is the first by a monarch since 1911. An unprecedented security operation is taking place with much of the centre of Dublin turning into a car free zone. Republican dissident groups have made it clear they are intent on disrupting proceedings. (Photo by Oli Scarff/Getty Images)
CORK, IRELAND - MAY 20: Queen Elizabeth II meets Fish Monger Pat O'Connell at the English Market on May 20, 2011 in Cork, Ireland. Queen Elizabeth II and Prince Philip, Duke of Edinburgh are on the final day of their historic four-day tour of the Republic of Ireland amid tight security, the first visit to Ireland by a British monarch since 1911. (Photo by Irish Government - Pool/Getty Images)
DUBLIN, IRELAND - MAY 18: Queen Elizabeth II and Prince Philip, Duke of Edinburgh are presented with a hurley during a visit to Croke Park on May 18, 2011 in Dublin, Ireland. The Duke and Queen's visit to Ireland is the first by a monarch since 1911. An unprecedented security operation is taking place with much of the centre of Dublin turning into a car free zone. Republican dissident groups have made it clear they are intent on disrupting proceedings. (Photo by Irish Government - pool/Getty Images)
DUBLIN, IRELAND - MAY 18: Irish President Mary McAleese (R), Queen Elizabeth II (C) and Christy Cooney (President of the GAA) during a visit to Croke Park on May 18, 2011 in Dublin, Ireland. The Duke and Queen's visit to Ireland is the first by a monarch since 1911. An unprecedented security operation is taking place with much of the centre of Dublin turning into a car free zone. Republican dissident groups have made it clear they are intent on disrupting proceedings. (Photo by Irish Government - pool/Getty Images)
DUBLIN, IRELAND - MAY 17: Police and protesters clash in the streets adjacent to the Garden on Remembrance where Queen Elizabeth II laid a wreath on May 17, 2011 in Dublin, Ireland. The Duke and Queen's visit is the first by a monarch since 1911. An unprecedented security operation is taking place with much of the centre of Dublin turning into a car free zone. Republican dissident groups have made it clear they are intent on disrupting proceedings. (Photo by Oli Scarff/Getty Images)
DUBLIN, IRELAND - MAY 18: Britain's Queen Elizabeth II speaks at Dublin Castle on the second day of her State Visit, on May 18, 2011 in Dublin, Ireland. The Duke and Queen's visit to Ireland is the first by a British monarch since 1911. An unprecedented security operation is taking place with much of the centre of Dublin turning into a car-free zone. Republican dissident groups have made it clear they are intent on disrupting proceedings. (Photo by John Stillwell - Pool/Getty Images)
DUBLIN, IRELAND - MAY 18: Queen Elizabeth II shakes hands with Brian O'Driscoll , Irish rugby captain before a State Dinner at Dublin Castle, on May 18, 2011 in Dublin, Ireland. The Duke and Queen's visit to Ireland is the first by a British monarch since 1911. An unprecedented security operation is taking place with much of the centre of Dublin turning into a car-free zone. Republican dissident groups have made it clear they are intent on disrupting proceedings. (Photo by Irish Government - Pool/Getty Images)
KILDARE, IRELAND - MAY 19: Queen Elizabeth II visits the Irish National Stud in County Kildare on May 19, 2011 in Kildare, Ireland. The Duke and Queen's visit to Ireland is the first by a monarch since 1911. An unprecedented security operation is taking place with much of the centre of Dublin turning into a car free zone. Republican dissident groups have made it clear they are intent on disrupting proceedings. (Photo by Oli Scarff/Getty Images)
DUBLIN, IRELAND - MAY 19: British Ambassador Julian King, President Mary McAleese, Queen Elizabeth II, Dr Martin McAleese, Prince Philip, Duke of Edinburgh and Taoiseach of Ireland Enday Kenny (back, R) at the Convention Centre on May 19, 2011 in Dublin, Ireland. The event held in the Convention Centre, attended by Queen Elizabeth II and Prince Philip, Duke of Edinburgh, will include a show of Irish Fashion, Music, Dance and Theatre. (Photo by Irish Government - Pool/Getty Images)
DUBLIN, IRELAND - MAY 18: Queen Elizabeth II and Prince Philip, Duke of Edinburgh visit the Guinness Storehouse and watch the pouring of a pint on May 18, 2011 in Dublin, Ireland. The Duke and Queen's visit to Ireland is the first by a monarch since 1911. An unprecedented security operation is taking place with much of the centre of Dublin turning into a car free zone. Republican dissident groups have made it clear they are intent on disrupting proceedings. (Photo by Irish Government - Pool/Getty Images)