Tens of thousands of people gathered at the Vatican last 7 September as Pope Leo XIV proclaimed the Catholic Church's first millennial saint, an Italian teenager dubbed "God's Influencer" for his efforts to spread the faith online.
London-born Carlo Acutis, who died of leukaemia in 2006 at the age of 15, was canonised in a solemn ceremony in St Peter's Square, with his family watching on.
Many young people were among the crowd, which the Vatican estimated at about 80,000.
"He was able to combine his everyday life -- school, football and his passion for IT and computers -- with an unshakeable faith," said Filippo Bellaviti, 17.
He told AFP the atmosphere was "beautiful", adding: "Seeing people from so many parts of the world, you can see the affection for Carlo for what he's done."
Pier Giorgio Frassati, an Italian mountaineering enthusiast who died of polio aged 24 in 1925, was also made a saint on Sunday.
Tapestries showing images of both young men were displayed on the facade of St. Peter's Basilica.
"Saints Pier Giorgio Frassati and Carlo Acutis are an invitation to all of us, especially young people, not to squander our lives, but to direct them upwards and make them masterpieces," Pope Leo said in his homily.
"Even when illness struck them and cut short their young lives, not even this stopped them nor prevented them from loving, offering themselves to God," he said.
The canonization of the so-called "cyber-apostle" has sparked interest across the globe, as his is not the traditional image of a Catholic saint.
His preserved body, which lies in a glass-walled tomb in the Italian town of Assisi, is starkly modern, dressed in jeans and a pair of Nike trainers.
Acutis's mother, Antonia Salzano, said her son was proof that "we are all called to be saints... everyone is special".