Prince William and Kate Middleton Send Save-the-Dates Via Fax

NEW YORK (CBS) Prince William and Kate Middleton have started sending out save-the-dates for their upcoming wedding - but don't expect to get one if you're not a member of a royal family, or if you don't own a fax machine.

Europe's major royal families have received faxes from Buckingham Palace asking them to keep April 29 open for the British prince's wedding.

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Britain's Daily Mail reports that while more traditional invitations will be sent to 1,800 guests by the Lord Chamberlain's Office next month, protocol dictates that sovereigns are given earlier warning than foreign heads of state and non-VIP guests.

Courtiers told the paper that the faxes were the most "efficient" way of informing people and have been used before for "large-scale" events.

King Constantine and Queen Anne-Marie of Greece received one of those save-the-dates, and will attend the event with their eldest son Crown Prince Pavlov. A spokesman told the Mail: "They received a fax in the last few days."

Prince Alexander and Princess Katherine of Serbia will also be there. They released a statement on their website as their RSVP, writing that they will be "delighted to attend."

Other royal houses, including Spain, Holland, Norway, Sweden, Denmark and Belgium, are expected to be invited. Royal spokesmen told the paper that the guest list was still being finalized.