Edmund of Langley, 1st Duke of York
Edmund of Langley, 1st Duke of York, KG (5 June 13411 August 1402) was the fourth surviving son of King Edward III of England and Philippa of Hainault.
Like many medieval English princes, Edmund gained his nickname from his birthplace: Kings Langley Palace in Hertfordshire.
He was the founder of the House of York, but it was through the marriage of his younger son, Richard of Conisburgh, 3rd Earl of Cambridge, to Anne de Mortimer, great-granddaughter of Edmund's elder brother Lionel of Antwerp, 1st Duke of Clarence, that the House of York made its claim to the English throne in the Wars of the Roses.
The other party in the Wars of the Roses, the incumbent House of Lancaster, was formed from descendants of Edmund's elder brother John of Gaunt, 1st Duke of Lancaster, Edward III's third son.
James FitzJames, 1st Duke of Berwick
James FitzJames, 1st Duke of Berwick, 1st Duke of Liria and Jérica, 1st Duke of Fitz- James( 21 August 1670 – 12 June 1734) was an Anglo- French military leader, illegitimate son of King James II of England by Arabella Churchill, sister of the 1st Duke of Marlborough.
Berwick was a successful general in the pay of Louis XIV of France.
Charles Lennox, 1st Duke of Richmond
Charles Lennox, 1st Duke of Richmond, 1st Duke of Lennox, 1st Duke of Aubigny( 29 July 167227 May 1723), of Goodwood House near Chichester in Sussex, was an illegitimate son of King Charles II by his mistress Louise de Kérouaille, Duchess of Portsmouth.
Richard Despenser, 4th Baron Burghersh
Richard le Despenser, 4th Baron Burghersh( 1396 – 1414) was the son and heir of Thomas le Despenser, 1st Earl of Gloucester( 1373 – 1400), by Constance of York.
Constance was a daughter of Edmund of Langley, Duke of York, fourth surviving son of Edward III of England, and Isabella of Castile, a daughter of Peter of Castile.
He was married to his 2nd cousin Lady Eleanor Neville( a granddaughter of John of Gaunt, a brother of Edmund of York), but died young without leaving issue.
His heir was his younger sister Isabel, who married successively Earl of Worcester, and then his cousin, Richard de Beauchamp, 13th Earl of Warwick.
His widow Eleanor, Lady Burghersh remarried to Henry Percy, 2nd Earl of Northumberland.
Isabella of Castile, Duchess of York
Isabella of Castile, Duchess of York( 1355 – 23 December 1392) was the daughter of King Peter and his mistress María de Padilla( d. 1361).
She accompanied her elder sister, Constance, to England after Constance's marriage to John of Gaunt, 1st Duke of Lancaster, and married Gaunt's younger brother, Edmund of Langley, 1st Duke of York.
Edward, 2nd Duke of York
Edward, 2nd Duke of York, , (– 25 October 1415) was an English nobleman and magnate, the eldest son of Edmund of Langley, 1st Duke of York, and a grandson of King Edward III of England.
He held significant appointments during the reigns of Richard II, Henry IV, and Henry V, and is also known for his translation of the hunting treatise "The Master of Game".
He was slain at the Battle of Agincourt, one of the principal military engagements of the Hundred Years' War against France, in 1415.
Richard of Conisburgh, 3rd Earl of Cambridge
Richard of Conisburgh, 3rd Earl of Cambridge( c. July 1385 – 5 August 1415) was the second son of Edmund of Langley, 1st Duke of York, and Isabella of Castile.
He was beheaded for his part in the Southampton Plot, a conspiracy against King Henry V.
He was the father of Richard Plantagenet, 3rd Duke of York, and the grandfather of King Edward IV and King Richard III.
Constance of York, Countess of Gloucester
Constance of York, Countess of Gloucester( – 28 November 1416) was the only daughter of Edmund of Langley, 1st Duke of York and his wife Isabella of Castile, daughter of King Peter of Castile and his favourite mistress, María de Padilla.
George Plantagenet, 1st Duke of Bedford
George of York, 1st Duke of Bedford( March 1477 – March 1479) was the eighth child and third son of Edward IV of England and Elizabeth Woodville.
He was a younger brother of Elizabeth of York, Mary of York, Cecily of York, Edward V of England, Margaret Plantagenet, Richard of Shrewsbury, 1st Duke of York and Anne of York.
He was also an older brother of Catherine of York and Bridget of York.
He was born in Windsor Castle in March 1477, and was created Duke of Bedford in infancy, probably in 1478, after the former holder of the title, George Neville, was deprived of the title by act of Parliament, ostensibly for lack of money to maintain the style of a duke.
He was appointed the Lord Lieutenant of Ireland in 1478, one of a series of nominal and largely absent lieutenants.
George died aged two.
This is considered likely to have been due to an outbreak of bubonic plague.
He was buried in St George's Chapel at Windsor Castle on March 22, 1479.
Philippa of Hainault
Philippa of Hainault (Middle French: "Philippe de Hainaut"; 24 June c.1310/15 – 15 August 1369) was Queen of England as the wife of King Edward III.
Edward promised in 1326 to marry her within the following two years.
She was married to Edward, first by proxy, when Edward dispatched the Bishop of Coventry "to marry her in his name" in Valenciennes (second city in importance of the county of Hainaut) in October 1327.
The marriage was celebrated formally in York Minster on 24 January 1328, some months after Edward's accession to the throne of England.
In August 1328, he also fixed his wife's dower.
Philippa acted as regent in 1346, when her husband was away from his kingdom, and she often accompanied him on his expeditions to Scotland, France, and Flanders.
Philippa won much popularity with the English people for her kindness and compassion, which were demonstrated in 1347 when she successfully persuaded King Edward to spare the lives of the Burghers of Calais.
This popularity helped maintain peace in England throughout Edward's long reign.
The eldest of her thirteen children was Edward, the Black Prince, who became a renowned military leader.
Philippa died at the age of fifty-six from an illness closely related to edema.
The Queen's College, Oxford was founded in her honour.

Question: Why did Edmund Of Langley, 1St Duke Of York's mother die?
Answer: edema