Fasti Ecclesiae Anglicanae 1066-1300, vi, 1-13, 31-36:
Sewal de Boville, master, was archdeacon of York by 16 January 1248, though he also occurs 1244×49. He was dean of York by 21 September 1249. His last occurance as dean was on 28 May 1255 when licence was given for his election to the archbishopric. In October of that year, he was elected archbishop of York and was consecrated on Sunday 25 July 1256. In May 1256 he was given a papal dispensation due to his illegitimacy. he died on 1 May 1258 and was buried in York Minster.