He had an illegitimate daughter
While attending university in Zurich, Einstein had a love affair with a fellow student, Mileva Marić, who would eventually become his first wife. Early in their relationship, however, the couple had a daughter named Lieserl before getting married, and with Mileva giving birth at her parent’s home in modern Serbia. After he birth, the couple never spoke about the daughter again, with many speculating that she either died in infancy, or was given up for adoption.