The Rt Revd David Conner, 71, is giving the address at St George's chapel at Windsor Castle.
The Dean of Windsor also conducted Harry and Meghan's wedding in May, although it was the Archbishop of Canterbury who married them and Bishop Michael Curry who delivered the address.
The reading just before his address is Colossians 3:12-16, which urges Christians do clothe themselves with compassion, bear with one another and be quick to forgive. Following his short talk, the congregation will sign the hymn 'Immortal, Invisible'.
Rt Rev Conner was the former Bishop to the Armed Forces but has been the Dean of Windsor since 1998, his role there also makes him one of the domestic chaplains to the Queen.
Previously, he studied at Oxford and he was the vicar at Great St Mary's Church in Cambridge and then became a suffragan Bishop in the Diocese of Norwich, consecrated by Lord George Carey, the then Archbishop of Canterbury.
In 2010 he was on the New Years Honours list and awarded Knight Commander of the Royal Victorian Order (KCVO).
Like Westminster Abbey, Windsor chapel is known as a Royal Peculiar, with the Dean of Windsor responsible only to the sovereign.
The church - a place of worship for the Queen and her family - is often at the heart of royal events, with the Windsors gathering there each year for Easter services, and in the past for occasions such as the service to mark the Duke of Edinburgh's 90th birthday.
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