Dr Rowan Williams said the pair had been forced to think long and hard about the pressures this will inevitably bring on their marriage, bearing in mind the disastrous track record of other royal couples.
But although he urged members of the public to pray for them, Dr Williams, who will conduct the ceremony at Westminster Abbey next Friday, said he was optimistic for the young couple’s future.
He praised the mature way in which they have approached their wedding and said it was clear how much exchanging vows meant to them. The outspoken Archbishop made his distinctly indiscreet comments in a pre-recorded interview released by Lambeth Palace yesterday.
It is understood that William and Kate have met Dr Williams privately on several occasions over the past few months.
Referring directly to their conversations, the Archbishop said: ‘William and Catherine are making this commitment very much in the public eye and they’re sensible, realistic young people.
‘They know what the cost of that might be. They’ve thought that through. And because of that they will need the support, the solidarity and the prayers of all those who are watching.’
In a clear reference to the failure of the marriages of William’s own parents, Prince Charles and Princess Diana, plus those of his uncle Prince Andrew and aunt Princess Anne, he added: ‘I want to wish William and Catherine every richest blessing in their life together.
‘But I want to wish them especially the courage and clarity they’ll need to live out this big commitment in the full glare – to live it out for the rest of us.
‘I hope they’ll be given the strength and the persistence to go on showing the rest of us what’s possible for the whole of their life together.’
The Church of England has already published a prayer asking for God’s help in keeping William and Kate faithful to each other. But Dr Williams expressed his confidence that the couple’s attitude to marriage bodes well for the future.
‘I’ve been very struck by the way in which William and Catherine have approached this great event,’ he said.
‘They’ve thought through what they want for themselves, but also what they want to say. They’ve had a very simple, very direct picture of what really matters about this event. I think that they have a clear sense of what they believe they’re responsible to.
‘They’re responsible to the whole society; responsible to God for their relationship. And I think it’s impressive that they’ve had that simplicity about it, they’ve known what matters, what’s at the heart of all this… because I think they are deeply unpretentious people.’
He also described how he felt about being involved in the big day, saying: ‘I’ve felt very privileged to be part of this event. Here are young people sending a message of hopefulness, sending a message of generosity across the world.’
A St James’s Palace spokesman said last night: ‘Any conversation Dr Williams may have had with Prince William and Catherine Middleton is a private matter.’