@Region Philbis,
Actually, King Charles was not "wrong." He simply used the English way of mentioning Magna Carta. That is why I prefaced my remark to Izzy with mention of him being English. In England, almost everyone who mentions Magna Carta refrains from using the article.
Sorta like most people in England mentioning being in the hospital refrains from using the "the" before hospital. Here in the US we would use the article in both cases.
We are not consistent for some reason. We would say, "He is in the hospital" for someone being a patient in a hospital. In England one would say, "He is in hospital." But we would say, "She is in school" (for a student) rather than "She is in the school."
In England one would say, "He/she is in hospital."