Albert Einstein's daughter whose fate is unknown was called Lieserl. She was the first child of Einstein and Mileva Marić, born in 1902 before the couple married. Her existence became known publicly only after letters between her parents were discovered in 1986.
The name Lieserl appears in Einstein and Marić's correspondence, but historians have never established the child's full legal name or certain fate. A 1903 letter mentions that she had scarlet fever, leading some researchers to believe she died as an infant. Other historians have suggested that she may have been placed for adoption, possibly with a family friend in Serbia.
Lieserl is often described as Einstein's “lost daughter,” but the nickname may originally have been a diminutive form of Elisabeth rather than her formal name. The uncertainty exists because there is no confirmed birth, adoption, death, or later-life record conclusively identifying her.