CANTERBURY, England (AP) — The new archbishop of Canterbury knocked three times on the doors of the city’s great cathedral on Wednesday, ceremonially demanding to be allowed inside in a tradition laid down over centuries by each new leader of the Church of England.

But this time, for the first time ever, a woman came knocking. And the doors were opened.

Sarah Mullally, a former cancer nurse who became a priest at the age of 40, walked into the cathedral to celebrate her historic election as the first female Archbishop of Canterbury since the post was created more than 1,400 years ago.

Although Mullally, 63, formally became archbishop in January, Wednesday’s event marked the beginning of her public ministry as both the head of the Church of England and spiritual leader of the worldwide Anglican Communion. The communion is an association of independent churches, including the Episcopal Church in the U.S., that together have more than 100 million members.

“We walk with God – trusting that God walks with us,” Mullally said in her first sermon as archbishop. “Trusting that — in all that we face, in the sorrow and the challenges as much as in the joy and the delight — we do not walk alone.”

The ceremony at Canterbury Cathedral was attended by Prince William, Princess Catherine, U.K. Prime Minister Keir Starmer and representatives from many of the 42 churches that comprise the Anglican Communion. Representatives from the Roman Catholic and the Orthodox church also attended.

In a nod to Mullally’s historic appointment, the service was held on the Feast of the Annunciation, which marks the moment Mary was told she had been chosen to be the mother of Jesus. It is a day on which the church says it celebrates “one of the great women of the Bible and thinks about how we can respond to God’s call.”