Neil Hall / Reuters A procession brings the Hungarian relic of St Thomas a Becket to a ceremony at Westminster Cathedral in London, Britain May 23, 2016.

A fragment of bone belonging to the murdered archbishop of Canterbury, Thomas Becket, has returned to England from Hungary for the first time in 800 years.

The relic is believed to be from the arm of Becket, slain at the altar of Canterbury Cathedral in 1170, after his relationship with medieval English King Henry II soured when he stood up for the church against the monarchy.

"The relic is to be the centerpiece of a week-long pilgrimage which finishes in Canterbury during the weekend of May 28 and 29," authorities said in a statement on the Cathedral website.

Neil Hall / Reuters Archbishop of Westminster Cardinal Vincent Nicolls (L) receives the Hungarian relic of St Thomas a Becket from Archbishop of Esztergom-Budapest Cardinal Peter Erdo before a ceremony at Westminster Cathedral in London, Britain May 23, 2016.

The bone, held in a gold case, is on a week-long loan from Hungary but it is unclear how it arrived in the eastern European country. British media said the fragment could have been taken when Becket was re-buried in the cathedral in 1220.

"It later became a symbol of Hungarian Catholic resistance to communism and is therefore of considerable importance for the Hungarian people," the Cathedral website added.

Neil Hall / Reuters Hugary's Presiedent Janos Ader and his wife Anita Herczegh view the Hungarian relic of St Thomas a Becket during a ceremony at Westminster Cathedral in London, Britain May 23, 2016.

Hungarian President Janos Ader and Cardinal Peter Erdo, the archbishop of Esztergom-Budapest, attended a Mass at Westminster Cathedral in London on Monday for Becket, who was made a saint by the Roman Catholic Church in 1173.

The fragment was then taken to the British parliament and Becket’s birthplace in Cheapside. It will be displayed in Westminster Cathedral and Canterbury Cathedral in Kent, southeast of London, before returning to Hungary.