Ukraine's Volodymyr Zelenskyy and Russia's Vladimir Putin could meet face to face in Turkey on Thursday.

If the proposed meeting in Istanbul goes ahead, it would mark only the second ever time the two leaders have sat down together.

The first was in 2019, when the two sides discussed an end to the fighting in Ukraine's eastern region of the Donbas, where Ukrainian troops had been fighting Russian-backed separatists since 2014.

It remains unclear what will unfold on Thursday and even if the leaders will show up - though Mr Zelenskyy said earlier this week that he would be .

Here is what happened last time Mr and Mr came face to face.

To try and end fighting in the Donbas region, Mr Zelenskyy and Mr Putin travelled to Paris in December 2019 for the Normandy Format Summit - an informal forum that was set up by French, German, Russian and Ukrainian diplomats after the conflict in the Donbas began.

It came after Mr Zelenskyy, who had , became Ukrainian president in May of the same year.

In the election, he beat Petro Poroshenko - a billionaire confectionery magnate and former Ukrainian foreign minister - who had met and spoken directly with Mr Putin on numerous occasions, but had failed to solve the conflict with Russia.

Alongside French president and then German chancellor , Mr Putin and Mr Zelenskyy sat opposite each other at a round table to discuss how they would end the conflict that had led to thousands of deaths.

The summit did lead to some agreements between the two nations. This included implementing "all necessary ceasefire support measures" before the end of 2019 and to release all prisoners of war.

Agreements were also made to disengage troops in three further areas of the Donbas region by the end of March 2020 - both Ukrainian troops and Russian-backed rebels had already pulled out of three frontline locations in the months before the meeting.

Both sides also said they wished to implement the political provisions of the , which were signed back in 2014 and 2015 as a first attempt to secure a ceasefire between the Ukrainian government and Russian-backed separatists.

The agreements included a roadmap for elections in the occupied regions of Luhansk and Donetsk and a plan to reintegrate the territory into the rest of Ukraine.

The 2019 meeting was seen at the time as an important step forward in ending the conflict, and some prisoner exchanges did take place, but it failed to provoke any real long-term change.

Russia and Ukraine continued to disagree on issues including the withdrawal of Russian-backed troops and elections in areas of Ukraine held by separatist rebels.

The summit then took place again in Paris in January 2022, but was instead attended by representatives of Russia, Ukraine, Germany and France, not the four leaders. In February 2022, senior diplomats met again, this time in Berlin, to try and find a way out of the conflict.

Weeks later, on 24 February, Russia launched its full-scale invasion of Ukraine.

In an address to the French parliament in March 2022, Mr Zelenskyy said the invasion had "ruined" the efforts of the Normandy Format.

If a meeting between Russia and Ukraine happens on 15 May, it is uncertain if Mr Putin will attend.

The meeting was first proposed by the Russian president, instead of accepting an unconditional 30-day ceasefire, but since the Kremlin has remained tight-lipped over who will travel to Turkey and whether it will include Mr Putin.

Ukraine's allies remained deeply sceptical about whether Mr Putin was serious about the talks. Russia has also continued its nightly attacks on Ukraine.

Unlike the 2019 discussions, America has been heavily involved in trying to secure peace between the neighbouring countries.

US President Donald Trump heavily encouraged Mr Zelenskyy to "immediately" accept the invitation to the meeting, going as far to say he is , if he thinks it would be helpful.

But Sky News US correspondent thinks the prospect of three presidents being in the same room is unlikely.

"If Putin and Zelenskyy were to meet, obviously, Trump would not want to miss out on the limelight there. But I am not going to put my money on it. At this stage, I just don't see Putin turning up," he said on the .

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Fellow Sky correspondent James Matthews added that Mr Trump's attitude towards the conflict is in stark contrast to the claim he made on the campaign trail that he could end the war in a day.

He said: "Beyond that campaigning bravado, Trump's stewardship over the diplomacy of the Russia-Ukraine conflict has been short of what he would have wanted.

"For all the warmth towards Putin, he has been given the cold shoulder in return... Publicly, he is talking about possibly getting on a flight, and it isn't the image of a president in control of events, it is the leader of the free world actually being led by events."