A host of European royals, including Crown Prince Felipe of Spain and Crown Princess Letizia of Spain, are expected at Pope Francis's inaugural Mass in the Vatican on Tuesday.
The Duke and Duchess of Gloucester will represent the UK at the celebration which marks the beginning of the Petrine Ministry of the newly-elected pope.
They will be joined by Prince Albert of Monaco and Princess Charlene of Monaco, Prince Willem-Alexander and Princess Maxima of the Netherlands, Grand Duke Henri and Grand Duchess Maria Teresa of Luxembourg, Prince Felix of Luxembourg and King Albert II and Queen Paola of Belgium.
The mass, which welcomes Argentinian Cardinal Jorge Mario Bergoglio, will take place in St Peter's Square at 9:30am. Much like the wait during the conclave to elect the Pope, thousands of Catholic supporters will gather inside the square to witness the ceremony which commemorates his entrance into office.
The 76-year-old is the 266th pope in the history of the Church and is the first Latin American Pope and Jesuit to reach the pontiff. His appointment was announced on the evening of the 13 March.
He appeared on the balcony of St Peter's Basilica just after 7pm to address the thousands gathered in the square.
His first words to the crowds were, "Brothers and sisters, good evening." He then thanked them for their welcome and led them in a prayer for his predecessor, Pope Emeritus Benedict XVI.
Shortly afterwards, @pontifex, the Pope's Twitter account, sent the first tweet of the new papacy. The message read, "HABEMUS PAPAM FRANCISCUM".
Prime Minister David Cameron was one of the first to tweet about the memorable event, saying: "A momentous day for the 1.2bn Catholics around the world as His Holiness Pope Francis I is appointed the 266th Bishop of Rome."
US President Barack Obama soon followed suit, sending "warm wishes" on behalf of the American people to the newly elected pontiff, hailing the Argentine as "the first pope from the Americas."
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