The Duke and Duchess of Cambridge may occupy only one of Kensington Palace’s apartments, but that doesn’t mean their home renovations are budget-friendly.

According to reports, Prince William and his wife of three years, Kate Middleton, both 32, have spent an estimated total of $6.6 million on refurbishing their four-story abode of some 20 rooms. While British taxpayers (via The Sovereign Grant) already shelled out $1.6 million for the renovations in 2013, new reports confirm the number has significantly grown — an increase which is said to be explained in an official report to be released Wednesday.

“This is the duke and duchess’ one and only official residence,” a spokesperson for the royal couple explained, adding, “It is here that they plan to stay for many, many years to come.”

Despite the refurbishment’s noticeable budget increase, a spokesperson for the royal family claims that the London home’s renovation costs were not reckless, saying the couple was "at pains to ensure that the specification is not extravagant.”

Kensington Palace Kensington Palace, the home of Britain's Prince William, his wife Catherine, Duchess of Cambridge in July 23, 2013. Photo: REUTERS

While Middleton (rumored to be pregnant with their second child) has been spotted busy shopping for home décor in recent months, a majority of the couple’s new furnishings is said to be provided by William’s father, the next in line to the throne, Prince Charles of Wales, 65.

According to a report from People magazine, renovations to the home’s kitchen and the nurseries were necessary due to the recent discovery of asbestos. A new roof, as well as modernized wiring and plumbing, were also reportedly required updates as the building was last overhauled in 1963. “Because it is a historic building, stringent guidelines must be adhered to in the renovations,” reads the report.

In November, Us Weekly reported that the apartment had been fitted to include encrypted Wi-Fi capabilities, central air and a "panic room."

The duke and duchess moved into their home, also known as Apartment 1A, in October 2013. The abode reportedly features five reception rooms, three bedrooms and three bathrooms, a night and day nursery for HRH Prince George (now 11 months old), staff bedrooms and “ancillary rooms.”