Pro-Russian separatist leader, Vyacheslav Ponomaryov, has confirmed that Western observers have been freed in the eastern Ukrainian town of Slaviansk and that there were no conditions for their release.
He said: "As I promised them, we celebrated my birthday yesterday and they left. As I said, they were my guests."
He confirmed that 12 people had been released, including Ukrainians and Europeans.
More top news
In the unexpected announcement on Monday, Mr Key said it was the "right time" to leave politics.
As the Government's Brexit appeal comes to the Supreme Court, here's a look at what you need to know.
According to local reports, the man was found by friends in their accommodation in Val Thorens resort in the Alps on Sunday morning.