Anonymous, History of the Arrival of Edward IV in England and the Final Recovery of His Kingdoms from Henry VI (online at the Richard III Society's American Branch site):
In the wynnynge of the fielde such as abode hand-stroks were slayne incontinent; Edward, called Prince, was taken, fleinge to the towne wards, and slayne in the fielde.
The Croyland Chronicler (online at the Richard III Society's American Branch site):
Upon this occasion, there were slain on the queen's side, either in the field or after the battle, by the avenging hands of certain persons, prince Edward, the only son of king Henry, the duke of Somerset, the earl of Devon, and all and every the other lords above-mentioned.
Sforza di Bettini Of Florence, Milanese Ambassador in France to Galeazzo Maria Sforza, Duke of Milan. June 2, 1471 (In Calendar of State Papers and Manuscripts in the Archives and Collections of Milan - 1385-1618--online here):
Yesterday his Majesty here heard with extreme sorrow, by clear and manifest news from England, so it appears, that king Edward has recently fought a battle with the Prince of Wales, towards Wales, whither he had gone to meet him. He has not only routed the prince but taken and slain him, together with all the leading men with him.
George, Duke of Clarence, to Henry Vernon, May 6, 1471 (in The Manuscripts of the Duke of Rutland Preserved at Rutland Castle, Vol. 1: Historical Manuscripts Commission, Twelfth Report, Appendix, Part IV).
Right trusti and welbeloved we grate you wele, lating you wite that my lord hath had goode spede nowe in his late journey to the subduyng of his enemyes, traitours and rebelles, of the which Edward late called Prince, the late Erl of Devon with other estates, knightes, squiers, and gentilmen, were slayn in playn bataill, Edmund late Duc of Somerset taken and put to execucion, and other diversee estates, knightss, squiers, and genlihnen taken.
Yorkist Notes: 1471 (From Charles Kingsford, English Historical Literature in the Fifteenth Century):
Eodem anno mensis Maii die iiijo Bellum iuxta Tewkysbury, vbi occisi fuerunt Edwardus, dictus princeps, filius Henrici sexti
Warkworth's Chronicle (online at the Richard III Society's American Branch site):
And ther was slayne in the felde, Prynce Edward, whiche cryede for socoure to his brother-in-lawe, the Duke of Clarence.
Chronicle of Tewkesbury Abbey (From Charles Kingsford, English Historical Literature in the Fifteenth Century)
Lord Edwarde, prince of Kynge Henry, in the felde of Gastum besyde Tewkesbery, slayne and buryed in ye mydste of y covent quiere in y e monastery ther : for whom god worketh.
Letter from the Mayor and Aldermen of the City of London to the Bastard of Fauconberg, May 9, 1471 (R. R. Sharpe, London and the Kingdom, Vol. 3):
Also Sir the saide Edward late called Prince Therle of Devynshire lord John of Somerset lord Wenlok Sir Edmund Hampden Sir Robert Whityngham, Sir John Lewkenore, John Delves w1 other moo were sleyne upon Saturday last passed at Tewkesbury.
A handwritten addition by Robert Cole in manuscript entitled Rental of all the houses in Gloucester (Robert Cole, Rental of all the Houses in Gloucester). Hammond suggests that the addition was made in 1472, hence the incorrect year of the battle:
This Kyng tooke to his wyfe Margarete, the Kyngus doujtur of Cicile,whit wham he had his sone Edward, Pryns of Wales, bat aftur bat he come from Fraunce with his modur with a gret ost was sley at be Batel by syde Tewkesbur[y], be yere of Oure Lord M1 CCCC. LXXII. [sic]
An entry in the Norwich register for 1470/71, cited by James E. Thorold Rogers in A History of Agriculture and Prices in England. As Rogers pointed out there and on a couple of occasions in Notes and Queries in the 1880's, the wording suggests that the prince did not fall in battle, but was tried before a military tribunal:
Ad guerram Tewkesbury, ubi adjudicatus fuit Edvardus filius Henrici nuper regis Anglix, et mater ejus capta.
Except for the Norwich account, which suggests that Edward of Lancaster was executed after a trial, all of these contemporary and near-contemporary sources (as well as Benet's Chronicle, which is in Latin and which I don't have access to at the moment) simply report that Prince Edward was slain; none implicates a particular person. (Even Warkworth simply says that Edward cried out for succor to the Duke of Clarence; it doesn't say that Clarence did the deed, and Clarence himself did not take credit for it in his letter.)
As Hammond points out, though, not long after the battle, another tradition began to develop: one where the prince, taken alive, is haled into the presence of Edward IV and killed. In 1473 in the "Histoire de Charles, dernier du de Bourgogne," for instance, the victorious Edward IV orders that the prince be disarmed, demands his sword, and strikes him across the face with it, after which everyone present joins in murdering the unfortunate prince. According to Hammond, other continental sources, long predating the Tudors, have Edward IV questioning the prince, who replies defiantly and is promptly killed by those present.
In the sixteenth century, the story of Edward of Lancaster being killed in the presence of Edward IV infiltrated the English accounts. As rendered in modernized English by Keith Dockray in Henry VI, Margaret of Anjou, and the Wars of the Roses: A Source Book, The Great Chronicle of London reports that both the prince and his mother, Margaret of Anjou, were taken to the king: "after the king had questioned a few words of the cause of his so landing within his realm, and he gave unto the king an answer contrary to his pleasure, the king struck him on the face with the back of his gauntlet, after which stroke so received by him, the king's servants rid him of his life forthwith."
With Polydore Vergil (whose account is available here), the Dukes of Gloucester and Clarence, as well as William Hastings, do the deed:
Two days later all these, save for Margaret and her son, paid with their heads in that same village. A little later Prince Edward, a very excellent young man, was taken to meet Edward, and was asked why he had dared invade his kingdom and trouble it with arms. He had the presence of mind to reply he had come to claim his ancestral realm. Edward made no response this, he only waved the lad away, and immediately those who stood around him (these were Dukes George of Clarence, Richard of Gloucester, and William Hastings) cruelly butchered him.
Edward Hall in Union of the Two Noble and Illustrious Families of Lancaster nd York adds Dorset, who was Elizabeth Woodville's eldest son, to the murderers:
After the felde ended, kyng Edward made a Proclamutio, that who so euer could bring prince Edward to him alyue or dead, shoulde haue an annuitie of an. C. 1. duryng his lyfe, and the Princes life to be saued. Syr Richard Croftes, a wyse and a valyaut knyght, nothing mistrusting the kynges former promyse, brought furth his prisoner prince Edward, beynge a goodly femenine & a well feautered yonge gentelman, whome when kynge Edward had well aduised, he demaunded of him, how he durst so presumptuously enter in to his Realme with banner displayed. The prince, beyng bold of stomacke & of a good courage, answered sayinge, to recouer my fathers kyngdome & enheritage. from his father & grandfather to him, and from him, after him, to me lyneally diuoluted. At which wordes kyng Edward sayd nothyng, but with his [hand] thrust hyin from hym (or as some say, stroke him with his gauntlet) whom incontinent, they that stode about, whiche were George duke of Clarence, Rychard duke of Gloucester, Thomas Marques Dorset, and Willia lord Hastynges, sodaynly murthered, & pitiously manquelled. The bitternesse of which murder, some of the actors after in their latter dayes tasted and assayed by the very rod of Justice
and punishment of God.
Ralphael Holinshed's version is similar to Hall's. It's interesting to note that none of the Tudor histories has Gloucester alone murdering Edward of Lancaster, but implicate Hastings (executed by Richard in 1483) and Dorset (a Woodville) as well, so while these accounts may be fanciful, they cannot be dismissed simply as Tudor attempts to blacken Richard III's name.
According to a Mr. Marshall who commented in Notes and Queries in 1882, Samuel Rudder in his 1779 New History of Gloucestershire writes, "The Prince of Wales is supposed to have been murdered in the house belonging to, an in the possession of, Mr. Webb, an ironmonger." I will have to take a look for that next time I am in the library.
The most peculiar version of the death of Edward of Lancaster, however, appears in a Flemish chronicle cited by Sir George Buck in his History of King Richard the Third. After recounting the scene where the prince mouths off to Edward IV, and Clarence, Dorset, and Hastings move in for the kill, Buck (per the edition edited by Arthur Noel Kincaid) adds,
And whereas it is said by the adversaries of the Duke of Gloucester that only he slew this prince with his sword, the contrary hereof is true. For I have read in a faithful manuscript chronicle written of those times that the Duke of Gloucester only, of all of those great persons, stood still and drew not his sword. And for this his forbearance there my divers good reasons be given. And first that it grew out of the mere conscience of honour and out of this heroical and truly noble detestation of base murders. And secondly because there was no need of any more swords, there being too many already drawn. For where there was need of his sword to defend the king his brother, there was no man's sword more ready. And chiefly, he abstained to be a fellow homicide in this act in regard of this prince's wife, who (as Johannes Meyerus saith) was in the room with him and was near akin to the Duchess of York, his mother, and whom he loved very affectionately, though secretly.
This account seems highly unlikely, as the contemporary sources that mention the matter are agreed that Edward of Lancaster's wife, Anne Neville, and his mother, Margaret of Anjou, were not found until several days after the battle and were brought to Edward IV at Coventry. It also seems rather implausible that Edward IV would allow Edward of Lancaster to be murdered in the presence of the 14-year-old Anne.
So how did Edward of Lancaster die? I'm inclined to believe the overwhelming majority of contemporary or near-contemporary accounts, which state that he met his death in battle, though it's rather a pity to sacrifice the story of the prince defiantly responding to the king before meeting what was certainly an inevitable death (had he not been killed in battle or while standing before Edward IV, he certainly would have been among the Lancastrian leaders beheaded on May 6, 1471). The stories of the prince being murdered in the king's presence, even if apocryphal, do, however, supply a useful moral to take through our lives: Don't Sass the King, or, alternatively, If You're Going to Die, at Least Speak Your Mind First.