It’s a document that finally conceded a monarch wasn’t beyond the law and King Charles’s Royal Family has been celebrating it and the powers it enshrined.

The Magna Carta of 1225 is considered the charter that finally put the crown under the control of law and as it reached its 800th birthday, a loyal cousin of The King was on hand to mark the moment.

The Duke of Gloucester was at the Society of Antiquaries of London to officially open a brand new exhibition focused on the 1225 Magna Carta and its role in English government and law.

The evening was a long way removed from the cold winter’s day when King Henry III sealed this Magna Carta. Prince Richard, who is descended from King Henry, joined guests on a summer’s evening in one of the prettiest parts of London as he opened the exhibition at Burlington House.

The 1225 version is considered pivotal even though it was the 1215 Magna Carta that marked a revolutionary moment in royal power. The first Magna Carta conceded that the Crown was not above the law but its signatory, King John, asked the Pope to revoke it just weeks later and got papal backing. John died soon afterwards and was succeeded by Henry III who was nine when he became king. Several more versions of Magna Carta appeared as his barons fought for power. In 1225, Henry was considered old enough to make his own decisions and on February 11 he sealed another version, considered the definitive one.

It’s become the basis for English law ever since.

The Society of Antiquaries is holding a series of special events marking the 800 years and the exhibition is a key strand of that.

On show are rare and important documents that outline how Magna Carta has impacted government and society for eight centuries. The exhibition, at Burlington House, is free and runs from July 23 until September 19 on Wednesdays, Thursdays and Fridays between 11am and 4pm. Entry is free and there’s no need to book.

The Society of Antiquaries isn’t the only place marking 800 years since this Magna Carta. There’s an exhibition on at Durham Cathedral which holds the only surviving copy of Magna Carta from 1216 as well as a version of the 1225 Magna Carta.