Queen Elizabeth II and Prince Philip, Duke of Edinburgh visit Hillsborough Castle on June 27, 2016 in Belfast, Northern Ireland.

Queen Elizabeth II and Prince Philip, Duke of Edinburgh visit Hillsborough Castle on June 27, 2016 in Belfast, Northern Ireland.

Prince Philip, Duke of Edinburgh arrives for a visit to Hillsborough Castle on June 27, 2016 in Belfast, Northern Ireland.

Queen Elizabeth II and Prince Philip, Duke of Edinburgh arrive for a visit to Hillsborough Castle on June 27, 2016 in Belfast, Northern Ireland.

Queen Elizabeth II and Prince Philip, Duke of Edinburgh arrive for a visit to Hillsborough Castle on June 27, 2016 in Belfast, Northern Ireland.

First Minister for Northern Ireland Arlene Foster arrives at Hillsborough Castle to meet Queen Elizabeth II and Prince Philip, Duke of Edinburgh (not pictured) on June 27, 2016 in Belfast, Northern Ireland.

Deputy First Minister Martin McGuinness arrives at Hillsborough Castle to meet Queen Elizabeth II and Prince Philip, Duke of Edinburgh (not seen) on June 27, 2016 in Belfast, Northern Ireland. 

Queen Elizabeth II attend the unveiling of the Robert Quigg VC memorial statue in Bushmills village on June 28, 2016 in Bushmills, Northern Ireland.

Queen Elizabeth II & Prince Philip, Duke Of Edinburgh attend the unveiling of the Robert Quigg VC memorial statue in Bushmills village on June 28, 2016 in Bushmills, Northern Ireland.

The unveiling of the Robert Quigg VC memorial statue in Bushmills village on June 28, 2016 in Bushmills, Northern Ireland. 

Britain's Queen Elizabeth II (L) and Britain's Prince Philip, Duke of Edinburgh are shown Giant's causeway, a world heritage site near Bushmills in Northern Ireland during a two-day visit.

Britain's Queen Elizabeth II is shown Giant's causeway, a world heritage site near Bushmills in Northern Ireland during a two-day visit on June 28, 2016.

Prince Philip, Duke Of Edinburgh attend the unveiling of the Robert Quigg VC memorial statue in Bushmills village on June 28, 2016 in Bushmills, Northern Ireland.

The Royal Guard attends the arrival of Queen Elizabeth II & Prince Philip, Duke Of Edinburgh at the unveiling of the Robert Quigg VC memorial statue in Bushmills village on June 28, 2016 in Bushmills, Northern Ireland. 

 Queen Elizabeth II attend the unveiling of the Robert Quigg VC memorial statue in Bushmills village on June 28, 2016 in Bushmills, Northern Ireland.

Secretary of state for Northern ireland Theresa Villiers attends the Queen Elizabeth II & Prince Philip, Duke Of Edinburgh arrival at he unveiling of the Robert Quigg VC memorial statue in Bushmills village on June 28, 2016 in Bushmills, Northern Ireland.

(R) Queen Elizabeth II attend the unveiling of the Robert Quigg VC memorial statue in Bushmills village on June 28, 2016 in Bushmills, Northern Ireland.

Queen Elizabeth II arrives on a steam train to open the new Bellarena Station village on June 28, 2016 in Bellarena, Northern Ireland.

 Prince Philip, Duke Of Edinburgh arrives on a steam train to open the new Bellarena Station village on June 28, 2016 in Bellarena, Northern Ireland.

 Prince Philip, Duke Of Edinburgh arrives on a steam train to open the new Bellarena Station village on June 28, 2016 in Bellarena, Northern Ireland.

 Prince Philip, Duke Of Edinburgh arrives on a steam train to open the new Bellarena Station village on June 28, 2016 in Bellarena, Northern Ireland.

Queen Elizabeth II arrives to open the new Bellarena Station village on June 28, 2016 in Bellarena, Northern Ireland.

 Queen Elizabeth II arrives to open the new Bellarena Station village on June 28, 2016 in Bellarena, Northern Ireland.

 Queen Elizabeth II arrives to open the new Bellarena Station village on June 28, 2016 in Bellarena, Northern Ireland.

Prince Philip, Duke Of Edinburgh arrives on a steam train to open the new Bellarena Station village on June 28, 2016 in Bellarena, Northern Ireland.

Queen Elizabeth II and Prince Philip, Duke Of Edinburgh arrive by steam train to open the new Bellarena Station village on June 28, 2016 in Bellarena, Northern Ireland. 

Queen Elizabeth II arrives to open the new Bellarena Station village on June 28, 2016 in Bellarena, Northern Ireland. 

Queen Elizabeth II and Prince Philip, Duke Of Edinburgh arrive on a steam train to open the new Bellarena Station village on June 28, 2016 in Bellarena, Northern Ireland.

Queen Elizabeth II and Prince Philip, Duke Of Edinburgh travel on a steam train from Coleraine Railway Station to Bellarena Station village on June 28, 2016 near Coleraine, Northern Ireland, United Kingdom. The Queen and The Duke of Edinburgh unveiled a plaque to mark the opening of the Bellarena Railway Station before they departed Northern Ireland.

Queen Elizabeth II smiles after arriving on a steam train to open the new Bellarena Railway Station after travelling from Coleraine Railway Station on June 28, 2016 in Bellarena, Northern Ireland, United Kingdom. The Queen and The Duke of Edinburgh unveiled a plaque to mark the opening of the Bellarena Railway Station before they departed Northern Ireland.

(L-R) Queen Elizabeth II and Secretary of state for Northern ireland Theresa Villiers smiles after arriving on a steam train to open the new Bellarena Railway Station after travelling from Coleraine Railway Station on June 28, 2016 in Bellarena, Northern Ireland, United Kingdom. 

Queen Elizabeth II arrives on a steam train to open the new Bellarena Station village after travelling from Coleraine Railway Station on June 28, 2016 in Bellarena, Northern Ireland, United Kingdom. 

 Queen Elizabeth II smiles after arriving on a steam train to open the new Bellarena Railway Station after travelling from Coleraine Railway Station on June 28, 2016 in Bellarena, Northern Ireland, United Kingdom.

Queen Elizabeth II and Prince Philip, Duke Of Edinburgh visit the Giants Causeway on June 28, 2016 in County Antrim, Northern Ireland, United Kingdom.

 Queen Elizabeth II and Prince Philip, Duke Of Edinburgh visit the Giants Causeway on June 28, 2016 in County Antrim, Northern Ireland, United Kingdom. 

Queen Elizabeth II and Prince Philip, Duke Of Edinburgh visit the Giants Causeway on June 28, 2016 in County Antrim, Northern Ireland, United Kingdom. 

Queen Elizabeth II and Prince Philip, Duke Of Edinburgh visit the Giants Causeway on June 28, 2016 in County Antrim, Northern Ireland, United Kingdom.

Queen Elizabeth II visits the Giants Causeway on June 28, 2016 in County Antrim, Northern Ireland, United Kingdom.

Queen Elizabeth II and Prince Philip, Duke Of Edinburgh visit the Giants Causeway on June 28, 2016 in County Antrim, Northern Ireland, United Kingdom. 

Queen Elizabeth II is escorted by guide Neville Mconachie during a visit to the Giants Causeway on June 28, 2016 in County Antrim, Northern Ireland, United Kingdom.