A missed moment right at the end of the show saw Princess Charlotte singing along to Diana Ross with her mum Kate.
The pair waved their Union Jack flags as they watched the performance, which was the closing moment of the show.
VIDEO: Princess Charlotte and Kate Middleton singing
Prince William and Prince George, meanwhile, enjoyed singing along earlier in the evening to Rod Stewart performing Sweet Caroline.
The Cambridges had enjoyed a busy day, having earlier gone to Cardiff ahead of the London show.
While George and Charlotte were in attendance, their younger brother Prince Louis, four, stayed at home.
Princess Charlotte and Kate Middleton are Diana Ross fans!
Kate's family, including her sister Pippa Middleton, were also at the show, with the mother-of-two debuting her baby bump for the first time.
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Other royals in attendance included Mike and Zara Tindall, who sat behind the Cambridges, Prince Charles and the Duchess of Cornwall and Prince Edward and the Countess of Wessex, along with their children Lady Louise Windsor and James Viscount Severn.
During the service, which celebrated the Queen's 70 years of service, the Prince of Wales paid tribute to both his mother and late father, Prince Philip.
As he spoke, images of Her Majesty that he had personally chosen flashed up behind him.
The Duchess of Cambridge and Princess Charlotte sang along to the performance
The speech had personal moments for Charles as well as he recounted watching the coronation of the Queen when he was just four years old, and also featured photos of his parents together back when they were both younger.
"Your Majesty, Mummy," he began. "The scale of this evening’s celebration – and the outpouring of warmth and affection over this whole Jubilee weekend – is our way of saying thank you – from your family, the country, the Commonwealth, in fact the whole world.
Princess Charlotte and Prince George both attended the Queen's Platinum Jubilee concert
"On behalf of us all, I wanted to pay my own tribute to your lifetime of selfless service. Your family now spans four generations. You are our Head of State. And you are also our mother."
He continued: "Your 'strength and stay' is much missed this evening but I am sure he is here in spirit… My Papa would have enjoyed the show and joined us wholeheartedly in celebrating all you continue to do for your country and your people."
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