Alexei Navalny – the prominent Russian opposition leader and staunch critic of President Vladimir Putin – has died in prison at the age of 47, RadarOnline.com can report. Navalny was serving a 19-year sentence on charges of extremism when he suddenly fell ill after a walk, according to the Federal Penitentiary Service. Despite attempts to revive him, he lost consciousness and passed away. The cause of death is currently under investigation. Navalny’s death has sparked widespread outcry and calls for an independent investigation. His spokesperson, Kira Yarmysh, expressed disbelief and stated th…