The Cross of Wales, which will be used at the head of the coronation procession in Westminster Abbey, incorporates fragments from the cross on which Jesus was crucified.
Pope Francis gave the relics, known as the True Cross, to King Charles as a coronation gift.
The cross incorporates Welsh materials, including slate, reclaimed wood, and silver from the Royal Mint in Llantrisant.
King Charles himself hammered the hallmark onto the silver used in the cross. This announcement serves as a reminder that, alongside the pomp and pageantry, the coronation on 6 May will be a religious ceremony.
Silversmith Michael Lloyd created the cross and inscribed it with the words of St. David, who is the patron saint of Wales. It is a gift from King Charles to the Church in Wales.
The coronation will be an Anglican service, but the prominent inclusion of a gift from the head of the Roman Catholic church reflects the representation of other denominations and faiths.
The silver cross has two small wooden shards set into it. It is claimed that these relics originate from the cross on which Jesus was crucified.
People have venerated relics of the True Cross for centuries and have undertaken pilgrimages to churches where they hold such relics.
There has also been long-standing scepticism about the volume and authenticity of such relics and whether they could all come from a single cross.
Archbishop of Canterbury Justin Welby will conduct the service on 6 May. He has highlighted how the heart of the coronation is a religious ceremony, likening it to the ordination of a priest.
Newly-Published Official Souvenir Programme
The newly-published official souvenir programme includes a statement from the archbishop, who says that in the middle of all the “magnificence and pomp,” there is a moment of “stillness and simplicity” when he anoints the King with holy oil.
The archbishop says the anointing will see the King in a simple white shirt, rather than “robes of status”, and he says the King will be “in the full knowledge that the task is difficult and he needs help”.
The public has not previously seen this moment, and it did not feature in the television coverage of the coronation of the late Queen Elizabeth in 1953.
There has been speculation about whether or not it will be visible for next month’s ceremony, but current expectations suggest it will remain a private moment in the coronation proceedings.
Anti-monarchy groups oppose the coronation, and a survey on Tuesday raised questions about the level of support for public funding of the occasion.
The coronation is a state event, but a YouGov poll of 4,000 adults found that 51% were against the government paying for it, compared with 32% who supported state-funding, with the rest saying they “didn’t know”.
Among 18-24 year olds, 62% thought the government should not fund the coronation.
The government has not revealed the amount that it will cost until after the event.