defiant return to the spotlight at Saturday’s Trooping the Colour ceremony has taken a toll on her health, according to a royal expert.The Princess of Wales, 42, looked radiant as she joined the royal family for King Charles’ birthday celebrations on the Buckingham Palace balcony.But according to royal expert Katie Nicholl, the physical toll of the event impacted the royal’s health.“The princess has this sort of swanlike quality about her — she’s sort of gliding on the surface — but beneath the water, I think often she’s paddling quite frantically,” Nicholl told “Entertainment Tonight.” “I can only imagine that a huge amount of preparation and time and effort and energy will have gone into Saturday’s appearance.”“She was on her feet for a long period of time,” she continued. “There was a moment where she was watching the parade . . .
and was offered a seat, which she gratefully accepted.”“That’s just a bit of an acknowledgement that she is not as strong, not as fit, as she was before she went into this treatment,” Nicholl added.The Post has reached out to Kensington Palace for comment.On Saturday, the Princess of Wales delighted fans by appearing alongside her husband, Prince William, and King Charles to watch the traditional military flypast with her three children.After the Red Arrows shot past the palace, spraying the colors of the Union Jack flag behind them, Middleton and her family waved to the crowd below.Despite the fact that the mom of three is currently undergoing chemotherapy, Nicholl noted that Middleton, 42, “looked impeccable.”“If you didn’t know that she was going through cancer treatment, you would never have guessed,” she said. “I think a day like Saturday, where she knows the eyes of the world are on.