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 .