An ornate reliquary case of silver gilt, precious stones and crystal was completed for the religious artefact in 1870, and it has been kept at the Bar Convent in York for centuries.

A Latin inscription says it was given to an English knight from the Shirley family by Arnulphus, Patriarch of Jerusalem, for his “distinguished valour” during the Crusades.

This inscription was added between 1659-1662 when it was taken to St Omer in France for repair and authentication, however, the scrollwork on the case is believed to be much older.

Dr Hannah Thomas cleans a True Cross relic at The Bar Convent Living Heritage Centre in York

Studies of historical documents show it likely changed hands from the Shirley family in the 16th century, before coming into the family of a Jesuit priest who gave it to the convent in 1792.

There are a number of documents, including authentication certificates signed and sealed by Monseigneur Lequette, Bishop of St Omers, and Bishop Robert Cornthwaite, Bishop of Beverley, in 1867.

The convent wanted to show the relic in the 1860s for public veneration so it needed it to be authenticated by high-ranking Church officials.

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Dr Hannah Thomas, the first lay person to look after the convent’s collections, said: “The relic itself does not appear to be widely known beyond this religious community, however, it is clearly a significant piece that would certainly be of great interest to a wider audience.

“When researching the relic, however, there seemed to be lengths of time in its history that appeared to be lost, and previous research carried out in the 1860s was unable to ascertain how the relic had transferred from one family to another. Through this documentation, and thanks to modern technology, we have been able to piece together a likely, very complex, history of this True Cross relic.

“We are thrilled to be able to enrich our knowledge of this piece, which has been so well protected and admired for centuries. It is a centerpiece of our collections and remains an object of contemplation with both religious and historic significance.

“We considered Easter, and the anniversary of when it was first authorised for veneration, to be the most appropriate time to share this research and to highlight this special object.”

The relic goes on display at The Bar Convent - the oldest convent in England which is still in use - from April 2.

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