A British-born Italian boy who died of leukaemia in 2006 will become the first Catholic saint of the millennial generation on Sunday, in a ceremony led by Pope Leo in St. Peter's Square that is expected to attract tens of thousands of worshippers.
Carlo Acutis, who died aged 15, learned computer code to build websites to spread his faith. His story has drawn wide attention from Catholic youth, and he will now be elevated to the same level as Mother Teresa and Francis of Assisi.
Sunday's ceremony was originally set for April but was postponed after the death of Pope Francis. Leo, elected in May to replace Francis, will now preside at such an event for the first time.
Leo will also canonize Pier Giorgio Frassati, a young Italian man who was known for helping those in need and died of polio in the 1920s.
Acutis' mother, Antonia Salzano, told Reuters earlier this year that the heart of her son's appeal to Catholic youth was that he lived the same life as others who were teenagers in the 2000s.
"Carlo was an ordinary child like (others). He used to play, to have friends, and to go to school. But his extraordinary quality was the fact that he opened the door of his heart to Jesus and put Jesus in the first place in his life."
"He used this skill to spread the good news, the Gospel," she added. "He wanted to help people to have more faith, to understand that there is an afterlife, that we are (pilgrims) in this world."
Being made a saint means the Church believes a person lived a holy life and is now in Heaven with God.
Other saints who died at a young age include Therese of Lisieux, who died at 24 in 1897 and was known for promoting a "Little Way" of charity; and Aloysius Gonzaga who died at 23 in 1591 after caring for victims of an epidemic in Rome.
As Acutis progressed along the Church's official path to sainthood, his body was moved to a church in the hill town of Assisi in central Italy, where St. Francis was from, in line with Acutis' last wishes.
The new saint's final resting place, where Acutis is entombed with a wax mould of his likeness placed over his body, wearing his track top, jeans and trainers, has become a popular devotional site, attracting thousands of worshippers every day.