Britain's Independent Catholic News reports that Lord Windsor, whose godparents are the Prince of Wales and the late Archbishop of Canterbury, Lord Coggan, will become the first ever member of the Royal Family to marry at the Vatican.
He will also be the first ever member of the Royal Family to marry openly and legally within the rites of the Catholic faith since the Reformation.
A recent meeting of the Privy Council confirmed the Queen's approval of the wedding as required by British law.
The historic moment in relations between the Catholic Church and the British Monarchy will take place at the Church of Santo Stefano degli Abissini in the papal gardens behind St Peter's Basilica.
Bishop Alan Hopes, an auxiliary bishop in the Archdiocese of Westminster, will conduct the ceremony.
Lord Windsor converted to Catholicism in 2001 and by doing so automatically lost his rights of succession to the throne because of the notorious 1701 Act of Settlement that bars Catholics from becoming monarch.
The little known and publicity shy Lord Nicholas has since his conversion been very active in Church affairs, Independent Catholic News says.
He privately joined tens of thousands who queued for hours to file past the body at the lying in state of Pope John Paul II in April 2005.
He and his Cambridge educated wife, Paola, attend Mass regularly at Westminster Cathedral and Brompton Oratory.
In 1994, his mother, the Duchess of Kent, became the most senior member of the Royal Family to convert to Catholicism. Lord Nicholas's uncle's wife, Princess Michael of Kent, and his sister in law, the Countess of St Andrews, whilst Catholic from birth, both conducted civil marriages.
His father, The Duke of Kent, who is the Grand Master of the United Grand Lodge of Freemasons of England, is also expected to attend the Vatican ceremony.
The Duke and Duchess of Kent are best known in Australia for their role in presenting the trophies at the Wimbledon tennis tournament every year.
Spokesman for the couple, Mr Anthony Bailey said: "The wedding will be a small and strictly private family affair. It is expected that only immediate family members will attend."
Update: First Vatican wedding ever for British or English Royals
Reader, Marlene Eilers Koenig, author of the book, Queen Victoria's Descendants, advises that a simple check of history shows that the wedding of Lord Nicholas Windsor and Donna Paolo Doimi de Frankopan will be the first ever Vatican marriage of a member of the English or British Royal Families - and not just since the Reformation.
"Consider the facts," Ms Eilers Koenig writes, "400 years ago Great Britain did not exist. The Act of Union did not happen until 1707 (which means next year will be the 300th anniversary of Great Britain). So there was no such thing as a British royal."
Noting the difficulties of travel in earlier times, Ms Eilers Koenig says that Royals simply "did not go to Rome to get married".
Listing Royal Family members from the time of Henry VIII's excommunication around 1533, Ms Eilers concludes that "a Vatican marriage would have been impossible" for following members of the English and British Royal families.
Member of Royal Family to marry at the Vatican (Independent Catholic News, 31/10/06)
Queen Victoria's Descendants, Marlene A. Eilers
First Vatican wedding ever for British or English Royals (Marlene A. Eilers-Koenig)
LINKS (not necessarily endorsed by Church Resources)
Lord Nicholas Windsor (Wikipedia)
Lady Nicholas Windsor (Wikipedia)
Duke of Kent (Wikipedia)
Royalty (Wimbledon Tennis Club)
Duke of Kent (Burke's Peerage)
5 Jan 2007