Ireland's Michael D Higgins arrived in London today ahead of the first state visit by a president of the republic since it gained independence from neighbouring Britain.
The visit comes three years after Queen Elizabeth II made a groundbreaking trip to the republic, which helped to heal deep-rooted unease and put British-Irish relations on a new footing.
Higgins' return visit will be seen as an official sign of further progress following the hard-won peace in Northern Ireland, which remains part of the United Kingdom.
Such an exchange of visits would have been impossible even at the turn of the millennium.
Higgins was met at London Heathrow Airport by Viscount Hood, lord-in-waiting to the queen. The state visit formally gets under way tomorrow.
"We are at a very interesting point in history, when we have, following Her Majesty's visit to Ireland, such good relations between our people," Higgins said before taking off.
"My hope for the visit, at the end of it all, is that people will, in ever more numbers, come to share in experiencing the history, the present circumstances and culture."
For state visits, Britain summons up all its traditional pomp in a bid to cement cultural, diplomatic and economic ties.
Queen Elizabeth, 87, plays host at a castle or a palace and the red-carpet visits typically involve ceremonial events, lavish banquets, cultural visits and political talks.
