VATICAN CITY (AP) — Beginning a long farewell to his flock, a weary Pope Benedict XVI celebrated his final public Mass as pontiff, presiding over Ash Wednesday services hours after a bittersweet audience that produced the extraordinary scene of the leader of the world's billion Catholics explaining himself directly to the faithful.

The mood inside St. Peter's Basilica was somber during the Mass, as if the weight of Benedict's decision and the finality of his pontificate had finally registered with the thousands present. The basilica erupted in a rousing standing ovation as Benedict exited for the last time as pope, bringing tears to the eyes of some of those closest to him.

"We wouldn't be sincere, Your Holiness, if we didn't tell you that there's a veil of sadness on our hearts this evening," Cardinal Tarcisio Bertone, Benedict's longtime deputy, told the pope at the end of the service, his voice breaking.