The Queen is to welcome Colombia's president Juan Manuel Santos to the UK at the start of his official state visit.
Mr Santos and his wife Maria Clemencia Rodriguez de Santos are staying with the Queen at Buckingham Palace in London, and will be entertained at a lavish state banquet there this evening.
It is the first time a state visit to the UK has been carried out by a Colombian president and comes after Mr Santos was awarded the Nobel Peace Prize for his efforts to end one of the world's longest-running civil wars.
Mr Santos was hailed for his political courage over a peace deal with left-wing Farc (Revolutionary Armed Forces of Colombia) rebels, although the accord was narrowly rejected by Colombians in a vote.
More than 220,000 people - mostly civilians - were killed in 52-year long hostilities and more than eight million people were driven from their homes.
The Queen and the Duke of Edinburgh will formally greet Mr Santos and the first lady at a ceremonial welcome on Horse Guards Parade, watched by Prime Minister Theresa May, Foreign Secretary Boris Johnson and Home Secretary Amber Rudd.
The president and his wife, who last met the Queen at a private audience in 2011, will then join her and the Duke in a state carriage procession along The Mall to the palace.
They will also take tea with the Prince of Wales and the Duchess of Cornwall at Clarence House. Charles and Camilla already know the president and the first lady after they travelled to Colombia for an official visit in 2014 - made possible due to the improved security situation there.
Mr Johnson has spoken of how Britain is planning to further develop its links with Colombia in the wake of the peace efforts and the Brexit vote.
"Colombia is on the verge of a historic peace agreement and through our ongoing support for the country the UK is well placed to take advantage of the opportunities that will follow," he said.
He added: "As we leave the EU, Britain remains a bold and outward-looking nation, and we are forging a new global role and taking advantage of economic and diplomatic opportunities in the wider world, beyond Europe."
The president and first lady will later attend a state banquet for 170 guests in the palace ballroom. The London Eye will be lit up in yellow, blue and red - the colours of the Colombian flag.
Talks at Downing Street with Mrs May will be held on Wednesday in what is the first state visit since she became Prime Minister.
The president will also travel to Northern Ireland on Thursday to meet community leaders in Belfast and discuss the challenges of community reconciliation post-conflict.
Mr Santos, 65, is said to be a voracious reader, a film buff and an old friend of former PM Tony Blair. They co-authored a book in 1999 on the Third Way, the political philosophy followed by Mr Santos after its adoption by Mr Blair.
The president has pledged to donate his Nobel Peace Prize money to the victims of the conflict, and to deliver a peace accord by Christmas.
The first lady, known to her family as Tutina, is the mother of their three children Martin, Maria Antonia and Esteban.
She studied as a graphic designer and leads the humanitarian initiative Colombia Humanitaria, a state strategy that deals with natural and environmental disasters.