On 14 February 1265, during a parliament summoned by Simon de Montfort in the name of King Henry III, an announcement was made that the king had promised to keep Magna Carta. On 11 March a sentence of excommunication was pronounced by nine bishops in support of the Charter and other Montfortian acts, after which the chancery began to issue exemplars of an inspeximus of the 1225 Charter, for distribution to the counties. This was the first time that exemplars of the Charter drawn up officially by chancery staff had been distributed since 1225. No original exemplar is known to have survived, though several copies (listed here) have been found (and more might come to light).
For more on the 1265 confirmation of Magna Carta, see: Sophie Ambler’s Feature of the Month for March 1214 (‘Henry III's Confirmation of Magna Carta in March 1265') and David Carpenter's Feature of the Month for December 2014 ('Simon de Montfort's Changes to Magna Carta in his 1265 Parliament: The reliefs of the earl and the baron').