The Bishop of Durham has been officially confirmed as the next Archbishop of Canterbury, in an appointment that was widely expected.
The Rt Rev Justin Welby succeeds Dr Rowan Williams as the spiritual leader of the 77 million-strong Anglican Communion.
The former oil industry executive becomes the 105th holder of the post.
As he addressed the media, he began by saying a prayer and then joked that his appointment was "the best kept secret since the last Cabinet reshuffle".
He went on: "To be nominated to this post is both astonishing and exciting", and it was something "he never expected".
The clergyman, who has been Bishop of Durham for only a year, admitted that the last few weeks "have been a rather strange experience".
He added: "We are at one of these rare points where the tide of events is turning and the Church nationally, including the Church of England, has great opportunities to match its very great but often hidden strengths.
"I feel a massive sense of privilege at being one of those responsible for the leadership of the Church in a time of spiritual hunger when our network of parishes and schools, and above all people, means we are facing the toughest issues in the toughest places."
He told reporters that one of the biggest challenges was taking over from Dr Williams, who he claimed "will be recognised as one of the greatest Archbishops of Canterbury".
Bishop Welby also said he was "utterly optimistic about the future of the Church".
He added: "We'll certainly get things wrong, I certainly will. But the grace of God is greater than our biggest failures. We will also certainly get much right and do so already."
Bishop Welby takes over the leadership of an institution battered in recent years by rows over women bishops and gay priests.
Dr Williams' tenure has been marked by a bruising war between liberals and traditionalists in the Church of England and the wider Anglican Communion over the issue of homosexuality.
The new appointment also comes as the Church of England stands poised to give final approval later this year for the introduction of women bishops following several years of tortuous negotiations and the departure of some Anglican bishops to the Catholic Church.
The new archbishop, who was first ordained as a deacon in 1992, will also have to face declining Church congregations.
The Bishop of Chichester, Martin Warner, welcomed his appointment, saying he would bring "many gifts and a rich experience of life to this calling".
But he warned: "He faces a daunting task, but the priority he attaches to a spiritual life of prayer, to reflection on the Bible and dependence upon the holy spirit will sustain him, as will the love and support of his family and friends.
"To that support I add my own and my prayers for his future ministry."
Prime Minister David Cameron also welcomed Bishop Welby's appointment and he "wished him success in his new role".