The French playwright Jean Anouilh wrote the play Becket or The Honour of God / Becket ou l'Honneur de Dieu inspired by Archbishop Thomas Becket's conflict with king Henry II. (In 1964, five years after its premier on stage, the play was adapted into a film starring Peter O'Toole, Richard Burton and John Gielgud.) The Wikipedia article about the play contains the following unsourced statement:
It contains many historical inaccuracies, which the author acknowledged.
The corresponding article on the French Wikipedia makes no mention of these inaccuracies. The Spanish Wikipedia article makes the same claim about the historical inaccuracies, again without providing a source:
Contiene muchas inexactitudes históricas, que el autor ha reconocido.
(This translates to the same sentence quoted above from the English Wikipedia article.)
Assuming that the statement has not been made up, where did Jean Anouilh acknowledge that the play contains many historical inaccuracies.