Ukrainian President Volodymyr Zelensky will on Wednesday make his first visit to the United Kingdom since the Russian invasion of his country, Downing Street said.
The surprise trip will see Zelensky meet Prime Minister Rishi Sunak, visit Ukrainian troops who are being trained by British forces, and address Parliament.
Zelensky's visit to London is only his second outside his country since Russia invaded Ukraine almost a year ago, following his visit to Washington DC in December.
UK Prime Minister Rishi Sunak meanwhile announced that his country will expand training to fighter pilots and marines while also promising a long-term investment in Ukraine's military.
Sunak said: "President Zelensky's visit to the UK is a testament to his country's courage, determination and fight, and a testament to the unbreakable friendship between our two countries.
"Since 2014, the UK has provided vital training to Ukrainian forces, allowing them to defend their country, protect their sovereignty and fight for their territory.
"I am proud that today we will expand that training from soldiers to marines and fighter jet pilots, ensuring Ukraine has a military able to defend its interests well into the future."