joint Lieutenant-Special and Captain General in France and Brittany 1374
Constable of Dover Castle and Warden of the Cinque Ports 1376-1381
Chief Captain of the Army for Portugal 1381-2
Chief Justice of Chester and Flintshire 1385-7
Guardian and Lieutenant of England 1394-5, 1396
Castellan of Mortagne-sur-la-Gironde 1396
Keeper of Fremantle Park 1397
Steward of England 1399
Master of royal mews and falcons
Knight of the Passion of Jesus Christ
Born: 5 June 1341 at King's Langley Palace in King's Langley, Hertfordshire, England. 
Controversy regarding paternity: A 2014 Y-DNA study compared the DNA of Edward III’s descendants, namely Richard III and 5 men descended from Henry Somerset, 2nd Earl of Worcester.  Richard III descended in the male line from Edward’s son Edmund of Langley, and Henry Somerset descended in the male line from Edward’s son John of Gaunt. The Y-DNA did not match. The press sensationalized the announcement to suggest that Edward III might not be the father of Edmund of Langley or John of Gaunt, or even of his other children. 
However, this is an extremely poor analysis of the data. Certainly, there was a non-paternal event(s) somewhere in the line down to his gr-gr—grandson Richard III, or somewhere in the 24 to 26 generation descent in the Somerset lines. It is not possible to tell where the non-paternal event occurred from this study. At this point, all the children of Philippa of Hainault must be presumed to be the children of Edward III, King of England.
Marriage and Children
Married:1st - Isabel of Castile-Leon, daughter of Pedro I 'the Cruel', King of Castile and Leon by Maria Diaz de Padilla in September 1371 at Roquefort near Bordeaux, France. A second ceremony was held on 1 March 1372 at Hertford Castle in Hertford, Hertfordshire, England.  She died 23 December 1392.
Married:2nd - Joan Holand, daughter of Thomas de Holand and Alice de Arundel, before 4 November 1393. They had no children.
Children of Edmund of Langley and Alice de Arundel: 
Edward of York. Born about 1374 (age 28 in 1402). Married Philippe Mohun before 7 October 1398. Slain at the battle of Agincourt on 25 October 1415. No children.
Constance of York.
Richard of York. Born about 20 July 1385 at Conisbrough Castle. He married 1st Anne Mortimer and 2nd Maud Clifford. Attainted and beheaded on 5 August 1415.
Death and burial of Edmund of Langley
Died: 1 August 1402 at King's Langley, Hertfordshire, England. 
Burial: Church of the Friars Preachers in King's Langley, Hertfordshire, England. 
From: Royal Tombs of Medieval England - "The fifth son of Edward III and Philippa of Hainault, Edmund was born at the royal manor of Langley in 1342 and died there on 1 August 1402. The duke was buried in the nearby priory church (Friars Preachers), as instructed by his will dated two years earlier. King's Langley was a Dominican house founded by Edward II in 1308 in the grounds of the royal manor-house, the result of a vow made when he was in 'great peril', most likely illness. Edward III took control of the building works in 1360, but the priory was still incomplete in 1399. Edmund's wife, Isabella of Castile, had been buried at King's Langley in 1394 on instructions from Richard II; according to Dugdale, Isabella's will left her burial-place to the king's discretion. There are no records of the King's Langley tombs. The priory surrendered to the crown in 1536, but was not dissolved until 1559, when the estate passed into private hands. The heraldic tomb-chest now standing in the north chapel of the King's Langley parish church is thought to have originated from the priory, and is usually ascribed to Edmund Langley, being moved to its present position in 1877. There is no effigy or inscription. The chest was executed in Purbeck marble with alabaster panels. In 1877 the tomb-chest was opened and found to contain the disturbed remains of a male about sixty and a female around forty, thought to be Edmund and Isabella." 
↑ e.g. Knapton, S. (2014, December 02). Richard III DNA shows British Royal family may not have royal bloodline. Telegraph. www.telegraph.co.uk (Note Elizabeth of York's claim was through Lionel of Antwerp, not John of Gaunt.)
It may be possible to confirm family relationships with Edmund by comparing test results with other carriers of his Y-chromosome or his mother's mitochondrial DNA.
Y-chromosome DNA test-takers in his direct paternal line on WikiTree:
Back in November 2014, a Plantagenet profile was merged into profile York-1256. York would not have been his surname at birth, because he didn't become the 1st Duke of York until he was an adult. Needs to be changed back to Plantagenet.