Prince William Playfully Teases Prince George and Princess Charlotte at Coronation Concert — See the Cute Pics

The royal was in “dad mode” as he joked around with his two eldest kids in the stands

Prince William showed off his playful dad side when he and Kate Middleton and their two eldest children, Prince George, 9, and Princess Charlotte, 8, joined the royal family at Sunday's Coronation Concert.

While waving small hand-held Union Jack flags, the Prince of Wales decided to have a little fun with his children, brushing the flag against George's face to block his view of the crowd gathered on the grounds outside Windsor Castle.

William, 40, then reached across George to do the same to Charlotte, but his daughter showed off impressive reflexes as she ducked out of the way in time to dodge the flag. (Five-year-old Prince Louis did not attend the Coronation Concert, but he was on hand for the coronation festivities Saturday.)

The Wales kids put their flags to good use during the concert, waving them as they clapped along to acts. They seemed to light up when Miss Piggy and Kermit made a surprise appearance, saying they were looking for their seats in the royal box. Towards the end of the show, Kermit seemed to find his way to the box — waving a flag right in front of Prince Edward and Sophie, the Duke and Duchess of Edinburgh!

RELATED PHOTOS: The Royal Kids' Cutest Coronation Photos

Princess Charlotte also was spotted singing along to Katy Perry's performance of "Roar" as drones in the sky formed a lion — a key part of King Charles and Queen Camilla's coats of arms.

For his official duties at the concert, Prince William gave an emotional speech about his father — but couldn't help slipping into "dad" mode again with a punny joke.

Taking the stage after Lionel Richie performed, the heir to the throne began, "I want to say a few words about my father and why I believe this weekend is so important. But don't worry, unlike Lionel, I won't go on all night long," he joked in a nod to hitmaker's 1983 smash single, "All Night Long."

"As my grandmother said when she was crowned, 'Coronations are a declaration of our hopes for the future,' " Prince William said, quoting Queen Elizabeth's coronation speech from 1953. "And I know she's up there, fondly keeping an eye on us. She would be a proud mother."

Related: See the Best Photos from the Coronation Concert

On the subject of his father's coronation, the prince continued, "For all that celebrations are magnificent, at the heart of the pageantry is a simple message: Service ... My father's first words on entering Westminster Abbey yesterday were a pledge of service. It was a pledge to continue to serve. Because for over 50 years, in every corner of the U.K, across the Commonwealth and around the world, he has dedicated himself to serve others, both current and future generations, and those whose memory must not be neglected."

The Prince of Wales pointed to his father's longstanding passion for environmental conservation (something he even incorporated into the ceremony itself): "Take the natural world. He warned us of the risks to our planet's health long before it was an everyday issue. "

"Or the Prince's Trust. It has supported over a million young people, many from disadvantaged backgrounds, to realize their ambitions," he continued, referencing Charles' namesake charity, established 1976.

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"And, perhaps most importantly of all, my father has always understood that people of all faiths, all backgrounds, and all communities, deserve to be celebrated and supported," the Prince of Wales added, emphasizing his father's interest in and dedication to interfaith relations. "Pa, we are all so proud of you."

"I also want to express my pride and gratitude for the millions of people who serve, in the forces, in classrooms, hospital wards and local communities," William continued. "I wish I could mention you all. Your service inspires us, and tonight we celebrate you too."

"I commit myself to serve you all: King, Country and Commonwealth," he concluded. "God Save the King."

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