Edmund Beaufort , 2nd Duke of Somerset Edmund Beaufort , 2nd Duke of Somerset , KG ( 1406 – 22 May 1455 ) , sometimes styled 1st Duke of Somerset , was an English nobleman and an important figure in the Wars of the Roses and in the Hundred Years ' War . He also succeeded in the title of 4th Earl of Somerset and was created 1st Earl of Dorset and 1st Marquess of Dorset ( previously held by his father and later forfeited ) , and Count of Mortain . He was known for his deadly rivalry with Richard Plantagenet , 3rd Duke of York . Life . Edmund Beaufort was the third surviving son of John Beaufort , 1st Earl of Somerset and Margaret Holland . His paternal grandparents were John of Gaunt , Duke of Lancaster , and Katherine Swynford . His maternal grandparents were Thomas Holland , 2nd Earl of Kent and Alice FitzAlan . Alice was a daughter of Richard FitzAlan , 10th Earl of Arundel and Eleanor of Lancaster . Although he was the head of one of the greatest families in England , his inheritance was worth only 300 pounds . By contrast his rival , Richard , Duke of York , had a net worth of 5 , 800 pounds . His cousin King Henry VI ' s efforts to compensate Somerset with offices worth 3 , 000 pounds only served to offend many of the nobles and as his quarrel with York grew more personal , the dynastic situation got worse . Another quarrel with the Earl of Warwick over the lordships of Glamorgan and Morgannwg may have forced the leader of the younger Nevilles into York ' s camp . His brothers were taken captive at the Battle of Baugé in 1421 , but Edmund was too young at the time to fight . He acquired much military experience while his brothers were prisoners . He became a commander in the English army in 1431 . After his re - capture of Harfleur , and lifting the Burgundian Siege of Calais ( 1436 ) , he was named a Knight of the Garter in 1436 . After subsequent successes he was created Earl of Dorset ( 1442 ) and the next year Marquess of Dorset . During the five year truce from 1444 to 1449 he served as Lieutenant of France . In March 1448 he was created Duke of Somerset . As the title had previously been held by his brother , he is usually called the second duke . Somerset was appointed to replace York as commander in France in 1448 . Fighting began in Normandy in August 1449 . Somerset ' s subsequent military failures left him vulnerable to criticism from York ' s allies . Somerset was supposed to be paid £20 , 000 ; but little evidence exists that he was . He failed to repulse French attacks , and by the summer of 1450 nearly all the English possessions in northern France were lost . By 1453 , all the English possessions in the south of France were lost as well , and the Battle of Castillon ended the Hundred Years War . Power had rested with Somerset from 1451 and was virtually monopolized by him until the King went insane and York was named Lord Protector . York imprisoned Somerset in the Tower of London , and his life was probably saved only by the King ' s seeming recovery late in 1454 , which forced York to surrender his office . By now York was determined to depose Somerset by one means or another , and in May 1455 he raised an army . He confronted Somerset and the King in an engagement known as the First Battle of St Albans which marked the beginning of the Wars of the Roses . Somerset was killed in a last wild charge from the house where he had been sheltering . His son , Henry , never forgave Warwick and York for his father ' s death , and he spent the next nine years attempting to restore his family ' s honour . Family . Edmund Beaufort , 2nd Duke of Somerset married before 1436 [ probably , abt 1425 ] , Lady Eleanor Beauchamp , widow of Thomas de Ros , 9th Baron de Ros , daughter of Richard de Beauchamp , 13th Earl of Warwick and his first wife , Elizabeth de Berkeley , daughter and heiress of Thomas de Berkeley , 5th Baron Berkeley and Margaret de Lisle , 3rd Baroness Lisle . Eleanor was an older half - sister of Henry de Beauchamp , 1st Duke of Warwick and Anne Neville , 16th Countess of Warwick . Their unlicensed marriage was later pardoned on 7 March 1438 , and they had the following children :