Aiden Aslin, known as Cossack Gundi, a British national serving as a Ukrainian marine since 2018, surrendered to Russian forces in Mariupol on 12 April, his Twitter account reported.

The account claimed that his unit was left without any other option, as they had run out of food and ammunition due to the tight siege Russia had subjected the Sea of Azov port city of Mariupol to. Aslin had been serving in the 503rd Battalion of Ukrainian Naval Infantry. He is not a mercenary and had previously served with the YPG in Syria. The name "gundi" means villager in Kurdish. It is claimed, however, that he is merely one of many foreigners currently still inside Mariupol.

Surrenders are becoming more common in Mariupol as the city is cut off from supplies and the situation becomes increasingly hopeless. Russia has claimed that many foreign citizens are serving in the ranks of the Ukrainian defenders of the city, and is alleging it has intercepted communications in “six different European languages,” although this cannot be confirmed.

Russia has also claimed to have intercepted a conversation between Aslin and an unnamed American man who advises him on how to leave Mariupol in disguise. He claims that such an attempt to break out would be suitable for him, as the Russians know his face and are actively searching for him. This intercepted communication is, of course, unconfirmed and bne cannot vouch for its authenticity.

Aslin’s capture may be the first confirmed capture of a foreign fighter by Russian forces and certainly the most high-profile, with Aslin boasting large social media followings, including 62,000 on Twitter and over 12,000 on Telegram. His Instagram channel, which had tens of thousands of followers, has since been deleted.

Rumours about foreign fighters have spread like wildfire since the city was first besieged by Russian forces on March 2. Some have ranged from the plausible, such as the prevalence of Nato advisors and foreign mercenaries being trapped there, to the outlandish, such as rumours going viral on pro-Russian telegram channels that American lieutenant-general Roger Cloutier, former commander of United States Africa Command, is holed up in Azovstal and unable to leave. Fact-checking websites have rated this as false.

A video circulating on Twitter appeared to show an Afghan mercenary in the city, who it is claimed served in Ashraf Ghani's special forces prior to the collapse of the Afghan government in September of last year. The presence of non-European looking people was also cited by a Russian soldier fighting in the city in an interview with RT.

The presence of foreigners as well as some high ranking members of Ukraine's Azov Battalion, such as Svyatoslav Palamar, may explain the various attempts to try to break out some of the trapped combatants via helicopter, and it is also claimed via ship, from the city. Previous attempts to evacuate combatants from Mariupol via helicopter resulting in several of them being shot down. The Russian Ministry of Defence claimed that a Maltese flagged dry cargo ship had attempted to break through Russia's blockade of Mariupol on April 8 but did not succeed.

90% of the city of Mariupol, once the centre of Ukraine’s steel export industry, has been destroyed by bombardment. Ukrainian forces have retreated to the confines of the Ilyich Steel and Iron Works and the now infamous Azovstal Steel and Iron Works, which is subject to heavy artillery attack that has destroyed much of it.

It is unknown what will happen to Aslin. As previously stated, he is not a mercenary and so the laws of the Geneva Convention apply to him. His Twitter account claimed that he is hoping for a prisoner swap, although it is likely he will be used for political leverage, possibly between Russia and the UK.