Pope Emeritus Benedict XVI’s health has worsened due to his age, and doctors are constantly monitoring his condition, according to a statement from the Vatican. Pope Francis visited Benedict at the monastery on Vatican grounds where he has lived since his retirement in 2013, after asking the faithful to pray for him earlier in the day. “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,” said Vatican spokesperson Matteo Bruni. “The situation at the moment remains under control, constantly monitored by doctors.”

At the end of his Wednesday audience with the public in a Vatican auditorium, Pope Francis departed from his prepared remarks to say that Benedict is “very sick” and asked the faithful to pray for the retired pontiff. Francis didn’t elaborate on the specifics of Benedict’s condition. “I’d like to ask all of you for a special prayer for Emeritus Pope Benedict, who, in silence, is sustaining the church,” Francis said. “I remind you that he is very sick. Let’s ask the Lord to comfort him and sustain him in this testimony of love to the church to the very end.”

Benedict, who was the first pontiff to resign in 600 years, has become increasingly frail in recent years as he dedicated his post-papacy life to prayer and meditation. When he turned 95 in April, his longtime secretary, Archbishop Georg Gaenswein, said that while he was physically weak, he was still lucid. In one of his previously publicized visits, Pope Francis called on Benedict at the monastery four months ago, accompanied by new cardinals. At the time, a photo showed a thin Benedict clasping Pope Francis’ hand as they smiled at each other.

In his first years of retirement, Benedict attended a couple of cardinal-elevating ceremonies in St. Peter’s Basilica. However, in recent years, he has not been strong enough to attend these long services. He was elevated to the rank of cardinal in 1977 by Pope Paul VI and served as the Vatican’s doctrinal watchdog as Cardinal Joseph Ratzinger before being elected pontiff in 2005. Benedict’s decision to resign in 2013 was met with dismay by some traditionalists, but Francis praised it as a courageous acknowledgement that physical frailty prevented him from fully serving the world’s 1.3 billion Catholics.

In an interview with Spanish newspaper ABC earlier this month, Francis revealed that shortly after being elected pope, he wrote a resignation letter in case medical problems impeded him from carrying out his duties. He has a history of health issues, including a knee ligament problem that has required him to use a wheelchair or a cane. However, he played down this challenge in the interview, stating that “one governs with the head, not the knee.” The head of Germany’s bishops’ conference, Limburg Bishop Georg Baetzing, also joined in Pope Francis’ call for prayers for Benedict. “My thoughts are with the emeritus pope,” Baetzing said. “I pray for him and ask the Lord to give him strength and peace.”