Richard had an only sister, Isabel. Richard's mother, Anne Mortimer, died during or shortly after his birth, and his father the Earl of Cambridge was beheaded in 1415 for his part in the Southampton Plot against the Lancastrian King Henry V. Within a few months of his father's death, Richard's childless uncle, Edward, 2nd Duke of York, was slain at the Battle of Agincourt in 1415, and so Richard inherited Edward's title and lands, becoming 3rd duke of York. The lesser title but greater estates of the Mortimer family, along with their claim to the throne, also descended to him on the death of his maternal uncle Edmund Mortimer, 5th Earl of March, in 1425.
Richard had an only sister, Isabel. Richard's mother Anne Mortimer, died during or shortly after his birth, and his father the Earl of Cambridge was beheaded in 1415 for his part in the Southampton Plot against the Lancastrian King Henry V. Within a few months of his father's death, Richard's childless uncle, Edward, 2nd Duke of York, was slain at the Battle of Agincourt in 1415, and so Richard inherited Edward's title and lands, becoming 3rd duke of York. The lesser title but greater estates of the Mortimer family along with their claim to the throne, also descended to him on the death of his maternal uncle Edmund Mortimer, 5th Earl of March, in 1425