Pope Francis said on Wednesday that his predecessor, former pope Benedict is "very sick."

"I would like to ask all of you for a special prayer for Pope Emeritus Benedict, who, in silence, is sustaining the Church. Let us remember him," Pope Francis said.

"He is very sick, asking the Lord to console and sustain him in this witness of love for the Church, until the end."

In 2013, Benedict became the first pope in some 600 years to resign.

What has the Vatican said about the former pope's health?

A Vatican spokesperson said that the former pope's condition has worsened in recent hours and that Pope Francis went to see him.

The Vatican said that Benedict's condition was "under control," and that he was receiving constant medical care.

Rheinhard Marx, Archbishop of Munich and Freising, said that he was joining Pope Francis in prayer.

"When Holy Father Francis tells us to unite in prayer, we will do that today, especially with young Christians," Marx said.

Who is former pope Benedict?

Born as Joseph Ratzinger in the southeastern German state of Bavaria, he became leader of the Catholic Church in 2005.

Benedict, 95, lives in the Vatican.

Benedict cited his declining health as the reason for his resignation in 2013.

Pope Francis was known as a conservative intellectual, whose disciplining of Latin American priestss who promoted Marxist-influenced Liberation Theology earned him the nickname "God's Rottweiler."

The former pope has been at the center of sex abuse scandals involving the Catholic Church. Early this year, he admitted to giving false testimony in an investigation in the Munich archdiocese, which he said was unintentional.

Benedict apologized for scandals that emerged within the church and expressed "deep remorse," but denied personal wrongdoing.