Freed Belgian aid worker Olivier Vandecasteele lost 30 kg (66 lb) but not his sense of humour during over a year in an Iranian jail, his spokesman said on Saturday following his release in a prisoner swap.

Vandecasteele arrived back in Belgium on Friday from Iran where he had been accused of spying and sentenced earlier this year to 40 years in prison and 74 lashes.

He was swapped for Iranian diplomat Asadollah Assadi who had been imprisoned in Belgium in connection with a failed bomb plot.

Vandecasteele, 42, is doing well despite his prison ordeal, his spokesman and friend Olivier Van Steirtegem told reporters.

“Maybe it was the adrenaline of the moment, but when we saw him, he still had the friendliness, the sense of humour and the willingness to understand he has always had,” Van Steirtegem said.” But physically, not surprisingly, he really lost a lot of weight.”

He said Vandecasteele was not told by the Iranian authorities of his release and thought that they were transferring him to a new detention place on Friday morning.

“It was only when he arrived at the airport that he realised that something else was going on. So for him, obviously, it was an extremely hard – I’d say violent – transition from isolation, or near isolation in the prison where he was, to (seeing) his family.”

Belgium’s justice minister said at the time of Vandecasteele’s conviction that it was based on fabricated evidence and amounted to retribution for the prison term given to Assadi. The Iranian foreign ministry has said Assadi was illegally arrested.