Mikhail "Mischa" Semenov is the son of Philip Jennings and Irina Semenova and the half-brother of Paige and Henry Jennings. He was conceived in Russia before Philip joined the Directorate S program, when Philip was about 17. Philip did not learn of Mischa's existence until 20 years later. Mischa shares his father's real first name.
In Season Five he comes to the USA in an attmpt to meet his biological father. However Gabriel convinces him it's in everyone's best interest that he goes back home to Russia. There, he finds work in a factory and meets his paternal uncle, who takes him home with him.