President Michael D Higgins has arrived in London ahead of his State visit to the UK, which he said is "very important in many ways" and "it is important for both countries to engage in our shared past".
The President also said he is very, very honoured and privileged to represent the people of Ireland on the trip.
The Government jet carrying the President and his wife Sabina touched down at Heathrow Airport in London after it left Casement Aerodrome in Baldonnel at around 4pm.
Also on board were Tánaiste and Minister for Foreign Affairs Eamon Gilmore and his wife.
The President was greeted at the foot of the Government jet by Irish Ambassador to the UK Dan Mulhall.
Viscount Hood welcomed the Presidential party on behalf of Queen Elizabeth.
The Queen's Colour Squadron, from the Royal Air Force, lined a red carpet as the Irish delegation descended from the jet.
The State visit officially begins tomorrow, where President Higgins will meet Queen Elizabeth at Windsor Castle.
Speaking earlier, Mr Higgins said that progress in the Northern Ireland peace process should not be about forgetting the past.
Mr Higgins will spend four days on the extended visit as a guest of the queen, a sign he says is symbolic of the importance both countries place on the normalisation of relations more than 90 years after independence.
"The peace process is that, it is a process that comes after the formal agreement at one level.
"Ultimately it is an exercise in consciousness at the level of community," President Higgins said.
"The challenge is to hand to a future generation all of the prospects of the future. You are not inviting them to an amnesia about any deep dispute.
"There are a lot of very difficult memories and it would be to my mind wrong to suggest to anyone that you should as it were, wipe the slate clean.
"I think Her Majesty in coming to Ireland and addressing for example issues of relations between our two people was doing it the right way."
Although President Higgins travelled to events in London, Manchester, Liverpool and Scotland last year, these were not official visits.
Highlights of the visit beginning tomorrow will include an address the President will make to both Houses of Parliament - another first for an Irish head of State.
President Higgins has expressed gratitude for the extended visit and being invited to stay at Windsor Castle, where he will also get to view the colours of disbanded Irish regiments in the British army.
READ Tommie Gorman's blog on the significance of the State visit
Matters of State and Moving On - visit marks another milestone in Anglo-Irish relations