Around 1341 John Clanvowe was born in Gergest, Herefordshire.
Around 1380 John Clanvowe [aged 39], a close personal friend of Geoffrey Chaucer [aged 37], was probably one of the first to hear, and with his close friend William Neville may be the subject of, Chaucer's 'A Knight's Tale'.
Westminster Chronicle. Thirdly, concerning a certain Carmelite friar1, who, driven by some spur of folly, came to the king’s court with the intention of accusing the duke of Lancaster, namely that the duke of Lancaster had deceitfully and treacherously plotted the king’s death. Therefore, after this friar had one day celebrated Mass before the king in the chamber of the earl of Oxford, and had obtained permission to say to the lord king whatever he wished, the aforesaid friar immediately attacked the duke of Lancaster on this matter, and proceeded so sharply that the king, without examination, would have ordered the aforesaid duke to be killed. But the other nobles standing by the lord king utterly denied that this should be done, asserting that it would be unjust for anyone to be condemned without judgement. When he had heard these things, the king, like a wise man, promised that for the time being he would act according to their counsel. Therefore, just as Sir John Clanvowe [aged 43]2 had predicted, the friar at once feigned madness, took off his cloak and his shoes, threw them out through the window, and in every way did the things that madmen do. The king further asked the often-mentioned friar whether anyone was aware of this matter, or whether he alone knew it. To this the friar replied, "Indeed, Lord Zouche3 has full knowledge of this matter, and I well know that I shall die for this cause." The king again said to him, "Take parchment for yourself4 and make two indentured bills containing everything you wish to allege against any person. Give one to me, and you shall keep the other with you, and then we shall know what we are to do in this matter." But the friar was in some confusion, because the duke of Lancaster would have to answer the charges laid against him. And so the king, seeing this, ordered him to be kept in custody in the meantime, until he should deliberate with his council what ought to be done with him.
Tertio de quodam fratre Carmelita qui quodam stimulo fatuitatis ductus ad curiam regis accessit ea intentione ut ducem Lancastriæ accusaret scilicet quod ipse dux Lancastriæ dolose et proditorie mortem regis machinatus est. Igitur postquam frater iste quadam die coram rege in camera comitis Oxoniæ missam celebrasset obtentaque licentia dicendi ea quæ sibi placuisset domino regi, super hujusmodi re frater prædiectus ducem Lancastriæ instanter impetiit et tam acriter processit quod rex sine examinatione ducem prædictum juberet occidi. Sed alii ncbiles domino regi astantes id fieri omnino negabant asserentes iniquum fore ut quispiam sine judicio condemnaretur. His quoque auditis rex velut sapiens secundum consilium eorum se protunc facturum promisit. Igitur, secundum quod dominus J. Clanvowe prædixerat, statim simulavit furorem exuit se capa sua et calciamentis suis eaque per fenestram ejiciebat ac ea quæ furiosi sunt ipse per omnia agebat. Et ulterius interrogavit sæpedictum fratrem an foret aliquis hujus rei conscius vel ipse solus novit. Ad quem frater respondit. "Immo dominus Le Souche plenam notitiam haberet hujus materiæ et bene cognosco me moriturum pro ista causa." Cui iterum ait rex, "Sume tibi parcamentum ac facias duas billas indentatas continentes omnia quæ volueris objicere contra aliquam personam et tradas mihi unam et alteram habebis penes te, et tunc sciemus quid super hujusmodi faciemus." Sed frater quodammodo confusus erat eo quod dux Lancastriæ ad objecta sibi imposita respondere deberet. Rex itaque hæc videns jussit eum interim custodiri donee deliberaret se cum suo consilio quid secum agere deberet.
Note 1. The Carmelite Friar who made accusations against John of Gaunt was John Latimer.
Note 2. John Clanvowe, around 1341-1391, was a Welsh knight, and a personal friend of Geoffrey Chaucer. He died in 1391 on a journey to Constantinople with William Neville, who died two days later. They were buried together in a joint tomb discovered in 1913 in Istanbul's Arap Mosque.
Note 3. William Zouche [aged 32], 1351-1396, 3rd Baron Zouche of Harringworth in Northamptonshire. Married 1. in or before 1365 Agnes Green sister of Henry Green [aged 37] referred to in the note above, and 2. before 1396 Elizabeth Despencer.
Note 4. On the margin here is the note: "These two bills were afterwards drawn up according to what the said friar dictated while lying in his bed, and were produced and read aloud in full parliament. In them he confessed that Lord Zouche had fully known the whole matter of the said proclamation. Moreover, he affirmed in the aforesaid bills that the community of London and that of Coventry had also consented to the said proclamation."
4. On the margin here is the note: "Istæ duæ billæ postea secundum quod dictus frater jacendo in lecto suo dictavit fuerunt confectæ et in pleno parliamento adhibitæ et perlectæ. In quibus vero fatebatur ... sse dominum le Souche totam materiam dictæ prædicationis ad plenum scivisse. Insuper et affirmavit in billis prædictis communitatem Londoniæ et Coventrensem dictæ prædicationi etiam consensisse."
Patent Rolls. 12th February 1385. Commission to W. Bishop of Winchester [aged 65], Thomas, Bishop of Exeter, Richard, Earl of Arundel [aged 39], Robert, Earl of Oxford [aged 23], Thomas, Earl of Nottingham [aged 16], Hugh de Segrave [aged 89], treasurer of England, Simon de Burley [aged 45], under-chamberlain, Nicholas Brembre, mayor of London, John Clanvowe [aged 44] and Robert Plesyngton, knights, Master Walter Skirlawe, keeper of the privy seal, John Waltham, keeper of the rolls of Chancery, John Appelby, dean of St. Paul's, London, Richard Rounhale and Thomas Bacton, clerks,
In September 1389 the Scrope vs Grosvenor Case was brought to the Court of Chivalry. Up to that time two families, Scrope and Grosvenor, had been using the armorial 
Scrope Arms: Azure, a bend or.
Several hundred witnesses were called including John of Gaunt 1st Duke Lancaster [aged 49], Geoffrey Chaucer [aged 46], John Clanvowe [aged 48] and John Savile of Shelley and Golcar [aged 64].
On 3rd September 1386 Owain Glyndŵr Prince Wales [aged 27] gave evidence at the Church of John the Baptist, Chester [Map].
The Court decided in favour of Scrope.
Neither party was happy with the decision so King Richard II [aged 22] was called upon to give his personal verdict.
On 27th May 1390 he confirmed that Grosvenor could not bear the undifferenced arms.
As a consequence of the case the Grosvenor has for many years used the name Bendor for horses and nicknames.
On 17th October 1391 John Clanvowe [aged 50] died on a journey to Constantinople. His travelling companion William Neville died two days later. They were buried together in a joint tomb discovered in 1913 in Istanbul's Arap Mosque. Curiously on the tomb slab the arms of John and William are impaled.
Westminster Chronicle. It was reported at that time how the Saracens, in Turkey and elsewhere, had utterly destroyed the lands and places of the Christians and had made them tributaries. Nevertheless, they promised that, whether they wished to worship one God or many gods, or to observe whatever sect they chose, they might do so, provided only that they paid them the tribute without delay, which at times had been refused. Afterwards they besieged a certain town situated in Barbary1, or in Africa, which the Genoese had recently cunningly conquered and now held, together with the other Christians who were in it. Therefore several lords, noble knights, and valiant esquires from England sought licence from the king to cross there for the purpose of helping the aforesaid place. Among them the most notable named were: the Earl of Devon, Sir W. Neville, Sir John Clanvowe, the Master of the Hospital of St John, and other famous men who would by no means endure injury to their good reputation.
Divulgatum est tunc temporis quomodo Saraceni, in Turkeya et alibi, terras et loca Christianorum penitus destruxerunt et tributarios eos fecerunt. Tamen deum unum vel deos eos colere, aut qualemcunque sectam servare voluerint, promiserunt dumtamen cis tributa solverent indilate nonnunquam negata. Consequenter quoddam oppidum in Barbaria sive in Africa situatum, quod jam tarde Januenses callide conquisierant ac cum cæteris Christianis existentibus in co jam tenuerant, obsiderunt, unde nonnulli domini nobiles milites et armigeri valentes de Anglia petiverunt licentiam a rege illuc transire causa suceurrendi locum præfatum, inter quos fuerunt potissime nominati, scilicet comes Devoniæ, dominus W. Nevyle, dominus J. Clanvowe magister hospitalis sancti Johannis et alii viri famosi qui læsionem suæ bonæ famæ minime sustinerent.
Note 1. The Barbary Coast is modern Morocco, Algeria and Tunisia; possibly Libya. The town that was besieged was Mahdia, Tunisia, which gives its name to the 1390 Mahdia Crusade.