Pope Emeritus Benedict XVI is “very ill" and being monitored by doctors, the Vatican confirmed on Wednesday.
His successor Pope Francis has asked the faithful to pray for the retired pontiff so God will comfort him “to the very end.”
Francis didn't elaborate on the condition of Benedict, who was the first pope to retire in 600 years in February 2013.
The Pope went to visit his predecessor in the monastery on Vatican grounds where Benedict has lived since stepping down.
The 95-year-old has become increasingly frail in recent years as he dedicated his post-papacy life to prayer and meditation.
"Regarding the health conditions of the emeritus pope, for whom Pope Francis asked for prayers at the end of his general audience this morning, I can confirm that in the last hours, a worsening due to advanced age has happened," Vatican spokesperson Matteo Bruni said in a written statement.
"The situation at the moment remains under control, constantly monitored by doctors," Bruni added.
At the end of his customary Wednesday audience, Francis departed from his prepared remarks to say that Benedict is "very sick" and asked the faithful to pray for the retired pontiff.