Answer
Tsarevich Alexei Petrovich was the father of Peter II. Alexei was the son of Peter the Great and his first wife, Eudoxia Lopukhina. Alexei was initially groomed to succeed his father as Tsar, but he fell out of favor with Peter due to his opposition to his father's reforms. Alexei was imprisoned and tortured, and he eventually died in prison under suspicious circumstances.