Belgian aid worker <a href="https://www.thenationalnews.com/world/2023/04/27/vandecasteele-jail-conditions-in-iran-worsen-amid-rumours-of-prisoner-swap/" target="_blank">Olivier Vandecasteele</a> was on his way home on Friday after spending nearly 15 months in detention in Iran after an Oman-negotiated prisoner exchange with Tehran, according to senior officials from the two governments. Belgium's Prime Minister Alexander De Croo tweeted a picture of <a href="https://www.thenationalnews.com/world/europe/2023/01/11/prison-conditions-in-iran-threaten-health-of-olivier-vandecasteele/" target="_blank">Mr Vandecasteele, 42,</a> in which he appears to be standing in a military plane. The picture of the former detainee, dressed in a black jacket and a pink shirt, was accompanied by the caption: “Finally with us.” Iran's government announced in parallel that diplomat Assadolah Asadi had been freed from a Belgian prison, shortly after Oman said that it had mediated an exchange in its capital Muscat, without naming the prisoners involved. Mr Vandecasteele arrived in Oman on Thursday evening, according to Mr De Croo. He was welcomed by Belgian diplomats and soldiers before undergoing medical tests the next morning and departing for Belgium, where he is expected to arrive on Friday evening between 9pm and 10pm CET. Mr De Croo said in a video statement that Mr Vandecasteele's life “takes precedent” over all other considerations. “We do not abandon anyone in Belgium, especially not when they are innocent,” he said. He described his living conditions in prison in Iran as “unbearable”. Belgian officials and his family previously described Mr Vandecasteele's arrest and sentence of 40 years in prison and 74 lashes for espionage earlier this year as part of Iran's “hostage diplomacy”. Belgian government sources confirmed that they had exchanged Mr Vandecasteele for Asadi, a move that recently became possible after <a href="https://www.thenationalnews.com/world/uk-news/2023/03/03/belgium-court-opens-door-for-iran-prisoner-swap/" target="_blank">Belgian courts</a> ruled that a prisoner swap treaty could go ahead legally. Iran's Foreign Affairs Minister Hossein Amirabdollahian said in a tweet that Asadi would soon arrive in his home country. Mr Amirabdollahian added that the diplomat had been “illegally detained in Germany and Belgium for more than two years” and thanked Oman for its “positive efforts”. The Iranian also travelled via Oman before returning to Iran, according to Oman's Foreign Affairs Ministry. “The Sultanate of Oman appreciates the positive high level spirit that prevailed during discussions in Muscat between the Iranian and Belgian sides, and their commitment to resolving this humanitarian issue,” the ministry said. Mr Vandecasteele was arrested in Tehran in 2022. His family's spokesman told <i>The National</i> last month that the Belgian aid worker had recently been moved from solitary confinement to a shared cell. The spokesman, Olivier Van Steirtegem, expressed fears for <a href="https://www.thenationalnews.com/world/2023/04/27/vandecasteele-jail-conditions-in-iran-worsen-amid-rumours-of-prisoner-swap/" target="_blank">Mr Vandecasteele's health, </a>as he had lost 25kg in prison, lost all his toenails and suffered from ear, stomach and dental infections during his detention. Asadi was convicted on terrorism offences in 2021 and sentenced to 20 years in prison after he was found guilty of masterminding a thwarted bomb attack against an exiled Iranian opposition group in France. The group, called the National Council of Resistance in Iran, had tried to block the prisoner exchange, arguing that it encouraged Iran to take hostages to trade for jailed agents, and challenged Belgium's prisoner swap treaty with Iran. The treaty was suspended in December as a result, but Belgium's highest court <a href="https://www.thenationalnews.com/world/uk-news/2023/03/03/belgium-court-opens-door-for-iran-prisoner-swap/" target="_blank">upheld it in March, </a>paving the way for Mr Vandecasteele's and Asadi's freedom on Friday. The National Council of Resistance said in a statement shared with <i>The National</i> on Friday that it condemned the release of Asadi, whom it described as “the terrorist diplomat”. They said that the constitutional court in Belgium had stated in its judgment that the Belgian government should have informed them before Asadi's transfer to “have the opportunity to once again take the issue to the court”. “The Iranian resistance will continue to seek justice in Belgium and in the international arena to the extent possible,” the group said. Iran has detained numerous foreigners and dual citizens over the years, convicting and sentencing them in secretive courts in an attempt to use them as leverage in negotiations with other countries, the UN found in 2022. Iran, facing western sanctions over its nuclear programme, has been rocked by protests in recent months and has also been hit by economic strain. Oman's Sultan Haitham was already scheduled to visit Tehran this weekend before the announced prisoner swap.