She’s fighting fit.

Kate Middleton has left Windsor for the first time since undergoing planned abdominal surgery — with a friend of the future queen saying she is “on the mend.”

The Princess of Wales, 42, has been recuperating at the royal residence since she was discharged from the London Clinic on Monday, Jan. 29.

The mom-of-three spent close to two weeks at that hospital following an operation to treat an undisclosed condition.

She is now spending a half-term holiday with Prince William, 41, and their three children George, 10, Charlotte, 8, and Louis, 5, at Sandringham — 127 miles from Windsor.

“Catherine is recovering well,” an unnamed friend told the Daily Mail.

“She was looking forward to a change of scene and will be able to take it easy in Norfolk while the children let off steam with William.”

The tabloid reports that King Charles, 75, is also at Sandringham after undergoing his first cancer treatment earlier this week.

It’s unclear whether Kate and Charles will see each other as they battle their respective health conditions.

News of the pair’s health problems plunged the royal family into crisis late last month.

On Jan 17., Kensington Palace released a statement saying the princess had been admitted to the hospital for planned abdominal surgery and would be canceling all planned royal engagements until Easter.

Just hours later, Buckingham Palace released its own statement saying King Charles would also be hospitalized for treatment for an enlarged prostate.

This past Monday, however, the royal family’s problems worsened with an announcement that the king had been diagnosed with an undisclosed form of cancer.

Doctors detected the disease while treating the monarch for the enlarged prostate.