Retired Pope Benedict XVI will mark his 65th anniversary as a priest at a Vatican ceremony June 28 attended by Pope Francis amid fresh confusion over the roles played by the current and former pontiffs.

The Joseph Ratzinger Foundation, a Vatican-based foundation dedicated to promoting the works of the emeritus pope, said on its website Wednesday the ceremony would be held in one of the Vatican's main reception halls.

It will be a rare outing for the 89-year-old Benedict, who has largely kept to his promise upon retirement to remain "hidden" from the world in prayer.

His longtime aide, however, sparked a minor outcry last month when he declared Benedict hadn't abandoned the papal ministry with his resignation but had rather expanded it "with an active and a contemplative member."