London, UK - It was almost like old times: with a beaming smile, Kate Middleton delighted fans on Saturday as she watched the annual Trooping the Colour parade alongside her family. Now, palace insiders have revealed some surprising details about the big royal return.

Kate appeared in a white dress with black accents, hat, bow, and charming smile at the annual birthday parade for King Charles III (75) in London, despite her ongoing cancer treatment.

The Princess of Wales' participation was the biggest surprise of the day, as she had not been seen in public for almost six months.

With England proudly celebrating its king, Kate probably didn't want to miss out on the festivities.

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"It was literally a last-minute decision by the Duchess," a palace insider told BILD.

But that's not all: the 42-year-old is said to have made the decision late on Thursday afternoon "all by herself" and, above all, "without pressure from the palace."

The reaction of the rest of the royals was euphoric.

It's believed that Kate deliberately chose the date to symbolize the strength and importance of her family, as well as to avoid her children having to sit alone in the carriage from Buckingham Palace to Parade Square.

Of course, a public comeback like this, with all the smiling and waving, is enjoyable but also quite exhausting.

According to the royal insider, Kate watched the parade from a window but was unable to stand for long and had to sit down.

The parade has been watched standing up for around 230 years, so her move didn't go unnoticed.

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"Kate looked fragile," the source explained.

Still, she was fully there for her children, as always, calming the "very excited" Charlotte with a gentle stroke through her hair and warning a playful Louis to leave the curtain cord alone.

Such gestures often remind palace staff of the late Princess Diana, who always considered the welfare of her children on formal occasions before bowing to royal protocols.

According to the insider, Kate is not yet out of the woods but added, "She's on the right track."