Former pope Benedict XVI secretly left his residence in the Vatican to visit his brother in hospital in Rome, La Stampa daily said on Saturday.
The 85-year-old, who promised on his retirement to live "hidden from the world", was escorted in a car with blacked-out windows for an hour's visit with Georg Ratzinger in the Policlinico Gemelli hospital in the Italian capital.
Ratzinger, 89, who is a priest, was admitted to hospital after travelling to the Vatican from Germany to spend Christmas with the former pontiff, the daily said, without providing any further details.
The visit was Benedict's second excursion since he retired to the former monastery within the Vatican gardens in May, where he has kept a very low profile.
His first trip was to attend a concert in August at Castel Gandolfo, the papal summer residence where he stayed for two months following his resignation in February last year, the paper said.