Asbestos, discovered throughout the building, was removed. Significant internal work was done to the 20-room property, and the roof was replaced.
The cost to rehabilitate the previously "uninhabitable" wing: $7.6 million in taxpayer money, plus hundreds of thousands from Prince William and wife Kate's own coffer.
Public money financed "basic works," while William and Kate paid for additional features. A royal spokesman explained the distinction with an example: "Kensington Palace has a working kitchen provided by the Sovereign (public) Grant to support receptions and other public events which might be hosted there. There is also a much smaller family kitchen paid for privately by The Duke and Duchess of Cambridge."
A source from the royal household told CNN that Apartment 1a, which will also be used for official engagements, has "a very ordinary level of furnishing" and added "It's not opulent."
Apartment 1a, Kensington Palace, was previously occupied by the Queen's late sister, Princess Margaret.
Celebrity Families of 2014 [PHOTOS]