Ukraine has used a US Patriot air defence system to shoot down a Russian Kinzhal hypersonic missile, the Pentagon has confirmed.
But the claim has generated a lot of debate on social media, with many commentators saying there is no evidence to support the story.
Initially, the Ukrainians denied it, but the country's air force confirmed the strike hours later on social media – saying it happened on 4 May during a Russian night attack on Kyiv.
The claim stated a Kinzhal missile, launched from inside Russia by a MiG-31 Foxhound jet, was blown from the sky by a Patriot missile.
For Ukraine, it would be a double first – the debut of its Patriot air defence system and the first intercept of one of Russia's most advanced Kinzhal ballistic missiles.
Known as the 'Dagger', the Kh-47M2 Kinzhal is an air-launched version of the Iskander-M ballistic missile.
Russia claims the Kinzhal has a range of more than 2,000km, or 1,200 miles, and a speed just over 7,000mph.
Despite that speed, the Dagger isn't a true hypersonic cruise missile because it only achieves hypersonic flight for part of its trajectory, but its speed, combined with its ability to manoeuvre erratically in flight, makes it a hard missile to intercept.
But why are their doubts over the Ukrainian and US claims?
A video, featuring Kyiv's Major Vitali Klitschko, has prompted a lot of head scratching.
The footage has Mr Klitschko showing a German magazine the remains of the Kinzhal missile.
However, many are saying it's not a Kinzhal, but is actually a Russian BETAB 500 concrete piercing bomb – a 500-pound weapon used to penetrate hardened buildings and damage runways.
The US says it was told by the Ukrainians that the downed missile was a Kinzhal, a claim it verified – with some technical experts supporting the view.
A diagram is said to show the inside of the Kinzhal, including the unitary warhead, which does look very similar to the bomb-shaped object shown off by Vitali Klitschko.
But, if a Kinzhal travelling at Mach 3 was hit by a Patriot, surely there'd be no wreckage left?
Once again, that depends, the experts say, on which version of Patriot missile the Ukrainians used.
One type, known as PAC-2, has a proximity fuse designed to explode close to an incoming missile, showering it with shrapnel.
Experts say the PAC-2, which Ukraine reportedly has, might not have caused catastrophic damage.
Put together, the official version of events does seem plausible, even if it is not 100% proven.
And the Pentagon may well have had further intelligence about the launch, flight path and trajectory that it's not sharing.
If true, the downing of a Kinzhal would be a coup for Ukraine, with it estimated that Russia has launched around 50 of them so far, with Kyiv not being able to stop it so far.
Russian Defence Minister Sergey Shoigu has boasted in the past that the Kinzhal is impossible to detect or intercept.
That may well have been proven untrue, depending on who you believe.