In a call to the UK's outgoing prime minister, the president of Ukraine has highlighted the "special" support Boris Johnson gave his country.
Volodymyr Zelensky expressed sadness at Mr Johnson's resignation from his position as leader of Conservative Party.
Johnson emphasized the UK's "unwavering support" for Ukraine, and called Mr Zelensky "hero".
After a string of scandals including the breaking of his own Covid laws, he was forced to leave by a cabinet revolt.
Johnson made mention of UK support for Ukraine in his resignation speech.
Johnson stated, "Let me now say to the peoples of Ukraine that I know that the UK will continue our support for your fight for freedom for however long it takes."
Russian critics of Johnson welcomed his resignation. Dmitry Peskov, President Vladimir Putin's spokesperson, stated that he "really doesn't like us - [and] we [do] not like him either".
Mr Peskov stated that he hopes "more professional people" will replace Mr Johnson and his team.
The UK is a major donor of humanitarian and military aid to Ukraine and has imposed severe sanctions against Russian targets that are involved in war crimes or prosecuting them.
Since the start of the war on 24 February, Mr Johnson has been to Ukraine many times. His most recent visit was to Kyiv last month.
Following an unannounced walkabout in Kyiv with President Zelensky in April, Johnson promised to help Ukraine end "this tragedy".
After the resignation speech of the former prime minister outside Downing Street, Mr Johnson called Mr Zelensky by telephone.
Johnson will continue to be prime minister until his replacement in the Conservative Party leadership contest is elected, which is expected take several weeks.
A spokesperson for Downing Street said that Johnson stated in the call that "the UK would continue providing vital defensive aid to Ukraine" "for as long is necessary".
He thanked President Zelensky for "all he's done to stand up for freedom", and he replied by thanking the prime minster "for his decisive actions on Ukraine".
"The Prime Minister concluded the call by praising President Zelensky and saying that: "You're a hero. Everyone loves you," said the spokesperson for No 10.
According to the Ukraine's presidency, Mr Zelensky's entire office and all Ukrainians were grateful for his help during the call.
Mr Zelensky stated that "We have no doubts that Great Britain will continue to support us, but your charisma and personal leadership made it exceptional."
According to research from the Kiel Institute for the World Economy, the UK was the eighth-largest donor of aid to Ukraine as a percentage of its gross domestic product (GDP) between January and July.
Johnson, at a summit of NATO security alliance in June pledged another PS1bn military support to Ukraine.
According to the UK government, this funding boosted total UK military and economic support by PS3.8bn in one year.
Officials and politicians from Ukraine paid tribute to Johnson after he resigned.
Mykhailo podolyak, an advisor to Mr Zelensky said in a tweet that the prime minister had been "always at the forefront" of supporting Ukraine.
He stated that the prime minister had "began calling a spade, a spade" in his remarks and stressed the seriousness of war with Russia to international community.
"Today, we have all we need to defend our country," said Mr Podolyak.
"Weapons and partnership, coalition. We are grateful to Johnson for understanding that victory is a symbol of the future of Ukraine.
Oleksiy Goncharenko, a Ukrainian MP, said that the country is "infinitely thankful" for Mr Johnson's "all you have done to us."
"You will always be part of our history and will play a role in the future victory. "Thank you," said Mr Goncharenko.
