With her sister the Duchess of Cambridge expected to attend alongside her brother in law Prince William, the wedding of Pippa Middleton is set to be one of the most exclusive events of the year.
It is anticipated that the cream of high society will gather to witness Miss Middleton marry James Matthews, a hedge fund manager and heir to a vast Scottish property.
But it has now emerged that there could well be some uninvited guests at the Berkshire church of St Mark’s on May 20.
Recently published Church of England guidance on ‘celebrity weddings’ has revealed that ordinary members of the public could have the right to attend.
And that raises the prospect of unknown strangers rubbing shoulders with Prince William and the Duchess as the happy bride and groom make their vows.
Indeed locals are already said to be looking forward to turning up.
Andrew House, chairman of the parish council for the next door village of Bradfield, where Pippa was born and Catherine Middleton spent her early years, told The Sunday Telegraph: "It’s a rather nice thought that they might be able to attend. I’m sure there will be interest.”
The guidance, unhelpfully published by the Church of England a few weeks before the big day, states that "a marriage is a public ceremony which at the least all parishioners are entitled to attend".
The rules mean all residents of the parish of Englefield, which surrounds St Mark's Church, have - in theory at least - the right to attend the ceremony.
According to the document, Celebrity Marriages in Anglican Cathedrals and Churches, produced by the Church of England Synod's legal advisory commission, members of the public are entitled to attend "as long as there is available seating or standing room unless a genuine question of safety or security arises".
But even this could present the wedding's organisers with a dilemma.
While the document states the rules do not need to be followed if "a genuine question of safety or security arises", this is a health and safety provision, only designed to be enforced if the church becomes dangerously overcrowded.
Stephen Borton, an ecclesiastical law expert and chief clerk of the faculty office of the Archbishop of Canterbury, said: "The document is pretty clear. Parishioners and those on the electoral roll have the absolute right to attend services of public worship, and they can't be denied access.
"Marriages are not a private event, they are public.
“It is a parish church and if any of the parishioners or any of those on the electoral roll wished to attend, they could not legally be refused. That of course does not extend to those from outside, such as the press."
Mr House added: “Some people will no doubt want to wish the couple well, especially those Englefield parishioners who knew the Middleton family from when they lived in the area. Kate went to Brownies here and there are still people in the area who remember her.”
Although St Mark’s is sighted on the private Englefield Estate - owned by the family of Conservative MP Richard Benyon since the 17th century - it is understood that parishioners would still enjoy the right to attend what is a public service.
Church of England lawyers said that where parishioners need to cross private property to get to a public place of worship, a "church way" - normally an ancient footpath - has to be provided to guarantee access.
The event could even be open to those from outside the parish, though only if they are there to "raise genuine impediments to the formalisation of the marriage" - such as proof that one of the couple is underage or already married.
Church weddings have always been public events, but this is the first time the Church of England guidance on the subject has been published online.
The guidelines only emerged following a request from a curate attending a Church of England seminar.
The Englefield Estate said the marriage was a "private ceremony and we are not able to comment or provide any details".
A representative for the wedding itself said: "For security reasons we are making no comments on the private details of this wedding (being held on private property)."