Prince William and Kate Middleton won’t be able to live full-time in their lavish new Windsor home when they become king and queen, Page Six is told.

Aides last week briefed that Forest Lodge, valued at $21 million, will be the couple’s “forever home” — however, that’s not quite the case.

Although the sprawling property, which lies within the secure grounds of Windsor Castle, will give the Prince and Princess of Wales much more space — eight bedrooms compared to their current home’s four — they will still have to spend plenty of time at Buckingham Palace once William ascends the throne.

“They will have to have a London base,” Hugo Vickers, writer and friend of the royal family, told Page Six.

“Remember, when [Queen Elizabeth] was at Windsor when [then Prime Minister] Theresa May was

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