But they won't be the only ones to see in the wedding ceremony of the century. Meet the Archbishop of Canterbury, Dr. Rowan Williams, who will officiate on the big day.
1. He's a poet
The spiritual head of the Anglican Church of England, Williams, 60, was born and raised in Swansea, Wales and, like the Welsh hero Dylan Thomas, he enjoys writing poetry. He's published two books of poems and shares Prince William and Kate Middleton's love for Wales.
2. He's got a wife and kids
The Archbishop can also relate to Will and Kate on the marriage front. In 1981, he wed a theologian named Jane. And when he took up his current post, he became the first Archbishop of Canterbury in 130 years to have school-age children when he was enthroned. Rhiannon and Pip were 14 and 6 respectively when he was chosen to lead the 70 million Anglicans in 2002.
3. A man of the cloth – and a Simpsons fan
The Archbishop once expressed an admiration for Homer and the gang. He praised The Simpsons for being, "one of the most subtle pieces of propaganda around the causes of sense, humility and virtue."
4. An Archbishop with a rebellious streak
The self-described "hairy lefty" (who speaks five languages) demonstrated a rebellious side when he was arrested for protesting the presence of nuclear missiles in the U.K. in 1985. He was reciting psalms on the runway of an American airbase at the time.
5. He'll help counsel Wills and Kate
Along with the Bishop of London – a close friend of William's father, Prince Charles – he will help counsel the couple, talking about being faithful and coping with marital issues. Both church leaders and family members are hoping this will help them cope with the stresses of a marriage in the spotlight and avoid the pitfalls that lead to the divorces of several royal couples, including Charles and Diana and Prince Andrew and Sarah Ferguson.