The young couple announced its engagement in November (10) and is set to exchange vows at London's Westminster Abbey on 29 April (11).
But members of the royal family are required by law to gain the approval of the monarch under the Royal Marriages Act of 1772, and the notice of approval, known as the Instrument of Consent, was signed by the Queen on 9 February (11).
The document was made public on Thursday (21Apr11) - on the Queen's 85th birthday.
It in, she states her consent to the union of "Our Most Dearly Beloved Grandson Prince William Arthur Philip Louis of Wales, K.G., and Our Trusty and Well-Beloved Catherine Elizabeth Middleton".
The news comes a day after the bride-to-be's parents, Carole and Michael Middleton, met the monarch for the first time. The Middletons enjoyed a private lunch with the Queen and her husband, Prince Philip, at Windsor Castle on Wednesday (20Apr11).
And while the future in-laws were meeting for the first time, William and Kate were in Northamptonshire, visiting the tomb of the prince's late mother Princess Diana at Althorp House.