Alexei Navalny, Russia’s top opposition leader and President Vladimir Putin’s fiercest foe, has died in prison. That's according to the Federal Penitentiary Service. It said Navalny felt unwell after a walk on Friday and collapsed. Navalny's team had no immediate confirmation of his death. He was moved in December from his former prison in central Russia to to a “special regime” penal colony — the highest security level of prisons in Russia — above the Arctic Circle. Navalny was handed a 19 year prison sentence in August on extremism charges and had already been sentenced to nine years in two convictions. He was repeatedly locked up in solitary confinement.