Royal officials expressed disappointment that the planned dinner party at one of Britain's finest restaurants had to be switched to Frogmore House in Windsor Home Park.
Master chefs Michel and Albert Roux transferred the gourmet meal from their restaurant the Waterside Inn at Bray, near Windsor, to the privacy of the banquet hall at Frogmore.
The puzzle of exactly who told a national newspaper about the secret family birthday celebration at the Roux brothers' exclusive restaurant is now exercising the minds of courtiers.
Earlier, more than 1,000 people helped the Queen celebrate on her estate at Sandringham, Norfolk, by singing "Happy Birthday Your Majesty" as she left church with the Princess Royal. They also presented her with flowers and birthday cakes.