A London-born boy has become the first millennial saint, in a ceremony steeped in an ancient ritual presided over by Pope Leo on Sunday.

In his short life, Carlo Acutis created websites documenting miracles as a means of spreading Catholic teaching, leading some to nickname him God's influencer.

His canonisation had been due in late April, but was postponed following the death of Pope Francis.

More than a million people are estimated to have made a pilgrimage to the Italian hilltop town of Assisi where Carlo's body lies, preserved in wax.

Another pilgrimage site associated with Carlo Acutis that has seen an increase in visitors is Our Lady of Dolours Church in London, where Carlo was baptized in 1991.

To the side of the church, an old confession booth has been converted into a shrine to him, which contains a single strand of Carlo's hair. His family were in finance and working temporarily in London when he was baptized.

Carlo moved back to Italy with his parents, where he was known for his love of technology and video games. He created a website documenting miracles during his teenage years.

Sadly, he passed away at just 15 from leukemia. His mother has dedicated years advocating for his sainthood, sharing stories of miracles attributed to him.

Pope Francis attributed two miracles to Carlo Acutis, clearing the way for his canonisation. The timing of Carlo's recognition is seen as an effort to re-engage young people's faith by highlighting a relatable and modern saint like him.