Sinn Féin’s Martin McGuinness, Northern Ireland’s former deputy first minister, has died aged 66.
It is understood he had been suffering from a rare heart condition. His funeral will be in Derry on Thursday.
The former IRA leader turned peacemaker worked at the heart of the power-sharing government following the 1998 Good Friday Agreement.
The Queen is sending a private message to Mr McGuinness’ widow, Buckingham Palace confirmed.
The meeting was particularly symbolic as the IRA murdered the Queen’s cousin, Lord Mountbatten, while he was on holiday in the Republic of Ireland in 1979.
Colin Parry, whose 12-year-old son, Tim, died in an IRA bomb in Warrington in 1993, said that although he did not forgive the IRA or Martin McGuinness, he found him a man who was “sincere in his desire for peace”.
Mr McGuinness became deputy first minister in 2007, standing alongside Democratic Unionist Party leaders Ian Paisley, Peter Robinson and Arlene Foster.
He died in the early hours of Tuesday in a Londonderry hospital with his family by his side.
The Northern Ireland Assembly will be recalled on Wednesday due to Mr McGuinness’ death.
A visibly ailing Mr McGuinness stood down from his post in January to protest against the DUP’s handling of an energy scandal, in a move that triggered a snap election.
Sinn Féin president Gerry Adams said: “Throughout his life Martin showed great determination, dignity and humility and it was no different during his short illness.
“He was a passionate republican who worked tirelessly for peace and reconciliation and for the re-unification of his country.
“But above all he loved his family and the people of Derry and he was immensely proud of both.”
Sinn Féin’s northern leader Michelle O’Neill said: “I have known him since I was a child but I am honoured to have worked alongside him. He inspired me and many others.”
Prime Minister Theresa May said although she could never “condone the path he took in the earlier part of his life, Martin McGuinness ultimately played a defining role in leading the republican movement away from violence”.
“In doing so, he made an essential and historic contribution to the extraordinary journey of Northern Ireland from conflict to peace,” she added.
Former US president Bill Clinton said that as Sinn Féin’s chief negotiator, Mr McGuinness’ “integrity and willingness to engage in principled compromise were invaluable in reaching the Good Friday Agreement”.