VATICAN CITY — Retired Pope Benedict XVI endorsed Pope Francis’ mercy-filled ministry Tuesday during an unprecedented Vatican ceremony featuring a reigning pope honoring a retired one on the 65th anniversary of his ordination as a priest.

The ceremony in the Clementine Hall of the Apostolic Palace served in part to show continuity from Benedict to Francis amid continued nostalgia from some conservatives for Benedict’s tradition-minded papacy.

Francis had invited the entire Vatican Curia, or bureaucracy, to celebrate Benedict’s anniversary, and prelates turned out in force for the rare occasion.

While Francis presided, it was Benedict who stole the show with an off-the-cuff, mini-theology lesson sprinkled with Greek and Latin that showed that the mind of the German theologian is still going strong at 89.

In it, Benedict thanked Francis for letting him live out his final years in the beauty of the Vatican gardens, where he said he felt “protected.”

“Thank you, Holy Father, for your goodness, which from the first moment of your election has struck every day of my life,” Benedict said, speaking without notes. “We hope that you can go forward with all of us on this path of divine mercy, showing us the path of Jesus toward God.”

Benedict’s vote of confidence may help quell conservative criticism of the current pope.

Francis has recently dismissed new questions about the implications of Benedict’s resignation by insisting that there is only one pope — himself — and that Benedict had pledged his obedience to him on the day he resigned.

He told reporters he felt that Benedict “had my back” and was continuing to help the church through his prayers.