Donald Trump has arrived in Portsmouth to join the Queen and other world leaders to mark the 75th anniversary of the D-Day landings.
It is the US President's final day of his UK state visit.
Prime Minister Theresa May will host 15 world leaders from the countries who fought alongside the UK - including Prime Ministers from France, Germany, Australia and Canada.
The D-Day landings in 1944, during World War Two (WW2), were the biggest combined land, air and sea operation in history.
It's a key date in the story of WW2.
It happened on 6 June 1944 after five years of war with Germany. The whole operation was codenamed Overlord.
A massive military force set out from the UK towards France.
The Allied forces landed on the beaches of Normandy, in France, and started to break through the German army's defences.
There will be a commemoration ceremony in Portsmouth on Southsea Common, where the allied invasion set off from.
The Queen and Prince Charles will be in attendance.
Members of the armed forces and more than 300 veterans, who are all over 90 years old, will also attend the event in Portsmouth - one of the key launch points on D-Day.
All the leaders of the countries who are attending today will sign a pledge to ensure a conflict like the Second World War will never happen again.
It is called "the D-Day proclamation", and the 16 signatories - including the UK and the United States - will commit to working together to "resolve international tensions peacefully".
Following the commemorations, President Trump will fly to the Republic of Ireland.
He will hold a meeting with the Irish prime minister Leo Varadkar before he goes to his golf resort in Doonbeg.