Viktor Medvedchuk, Russian President Vladimir Putin’s closest ally in Ukraine, was captured on Tuesday during a “lightning-fast and dangerous” special operation, the head of Ukraine’s security service said.

Medvedchuk, 67, was charged with treason in May 2021, accused of selling military secrets to Russia and exploiting natural resources in Crimea, and escaped from house arrest not long after Russia invaded Ukraine in late February. It isn’t immediately known where Medvedchuk was found and how he was arrested.

In a video address posted to Telegram, Ukrainian President Volodymyr Zelensky said, “I propose to the Russian Federation to exchange this guy of yours for our boys and our girls who are now in Russian captivity.”

A Ukrainian politician made wealthy by Russian oil interests, Medvedchuk was part of the Opposition Platform – For Life coalition, which pushed a pro-Moscow agenda. Putin is the godfather of Medvedchuk’s youngest daughter, and after Medvedchuk was first arrested last year, Putin promised to “respond,” calling it a political persecution.

In January, the U.S. accused Medvedchuk and three other Ukrainian politicians of being involved in a scheme to set up a collaborator government should Russia invade the country, and put them under sanctions. In March, Medvedchuk’s $200 million yacht, the Royal Romance, was seized in Rijeka, Croatia.