Britain's Queen Elizabeth II shakes hands with Northern Ireland Deputy First Minister Martin McGuinness at the Lyric Theatre in Belfast, in a landmark moment in the Northern Ireland peace process, Buckingham Palace said.
Queen Elizabeth II shook hands with former IRA commander Martin McGuinness on Wednesday in a highly symbolic moment in the Northern Ireland peace process.
The initial handshake between the queen and McGuinness, who is now deputy first minister of the British province, took place behind closed doors in a Belfast theatre.
The two then shook hands a second time for the cameras as the queen left the building.
McGuinness held the monarch's hand for a few moments and she smiled as he spoke to her in Irish, telling her the words meant: "Goodbye and God speed."
When asked about the meeting later, McGuinness told reporters it had been "very nice", without elaborating.
The event is seen as an important milestone in Anglo-Irish relations after three decades of sectarian violence, known as "The Troubles", which largely ended with the Good Friday peace agreement in 1998.
A spokesman for British Prime Minister David Cameron said the handshake had "taken relations between the two countries to a new level".
It comes on the second day of the queen's visit to the province, which on Tuesday took her to Enniskillen, the scene of a notorious 1987 Irish Republican Army bombing which killed 11 people.
McGuinness was a senior commander in the IRA when the paramilitary group killed the queen's cousin Louis Mountbatten in 1979 by bombing his boat while he was on holiday in County Sligo in the Republic of Ireland.
His Sinn Fein party, the political wing of the now-defunct IRA, continues to reject British rule of Northern Ireland.
In the eyes of republicans, the queen is commander-in-chief of an army that killed 13 people during a civil rights march in 1972, an event known as Bloody Sunday.
Earlier this week McGuinness said that by shaking the queen's hand he would be "shaking the hands of hundreds of thousands of unionists".
The first handshake came in a brief meeting when they were joined by the queen's husband Prince Philip, Northern Ireland's unionist first minister Peter Robinson, Irish President Michael D Higgins and his wife Sabina.
It took place on the sidelines of a cross-border charity arts event at the Lyric Theatre, in a room with the curtains drawn.
Sinn Fein said McGuinness told the queen that their encounter, which comes a year after she made a landmark visit to the Republic of Ireland, was a "powerful signal that peace-building requires leadership".
In their meeting, McGuinness reportedly commented on the queen's visit to Dublin in May 2011 and the remarks she made then expressing her sympathy for victims on both sides of the conflict.
A Sinn Fein spokesman said: "He emphasised the need to acknowledge the pain of all victims of the conflict and their families."
Britain's Northern Ireland Secretary Owen Paterson said the event signalled "a shared future", noting that only a few years ago "none of this could have happened."
"After all the trauma of Northern Ireland, everyone is looking forward," he said.
Signs of the former tensions had resurfaced overnight, however, when around 100 missile-throwing youths clashed with police in Belfast, injuring nine officers.
Police said more than 20 petrol bombs were thrown in the Broadway area of the city.
Earlier there was unrest in the west of Belfast after Republicans erected a flag and sign saying "Eriu is our queen", referring to a goddess of Irish mythology.
The queen and Prince Philip had received a warm welcome, however, in Enniskillen, where flag-waving crowds of supporters lined the streets.
During the day they attended a service of thanksgiving at the city's St MacCartin's Church of Ireland Cathedral, along with Protestant and Catholic clergy.
Afterwards, in a potent gesture of conciliation, they stepped across the road to St Michael's Catholic Church. It is believed to be the queen's first visit to a Catholic church in Northern Ireland.
Later Wednesday the 86-year-old monarch and her husband were to join 22,000 guests for a garden party in the grounds of Stormont, Northern Ireland's parliament buildings.
The two-day trip is part of the queen's diamond jubilee celebrations, marking her 60th year on the throne and is her 20th visit to the province.