David, 41, performed at the star-studded concert alongside Ed Sheeran, Sir Rod Stewart and Diana Ross as part of celebrations to commemorate the late Queen Elizabeth II’s 70-year reign.
The “7 Days” crooner said he was invited with his mother to Buckingham Palace for a “little soiree” after the performance.
In a forthcoming appearance on The Jonathan Ross Show, which will air on Saturday 19 November on ITV, David revealed that the Prince of Wales told him how his eldest son felt about his outfit.
“[My mother] was gripping my hand and I could tell what she was going to say, she said, ‘We’re in the Queen’s house’,” he said.
“Prince William walks over, he comes over, says, ‘My son George was going crazy for the blue sequinned outfit you were wearing’.
“My mum was there, I said, ‘Lovely to meet you, love that George loved the outfit’. That moment for me, as a son [introducing my mother to William], was probably the most incredible moment for me.”
David continued: “Then Kate [Middleton] comes over. Very memorable moment.”
The R&B singer, whose eighth studio album 22 was released in September, said William was “super down-to-earth”.
“It’s almost like seeing him and seeing Harry and seeing the next generation coming through, I feel it’s giving a different tone to the royal family,” he added.
David also described King Charles III in the same way, as well as being a “stand-up guy”.
“I’m an ambassador of The Prince’s Trust,” he said, speaking about the King. “He is another one. He’s a stand-up guy. Whenever I met him, it’s not the pretence of what could come with being a royal.
“He’s very down-to-earth and he is very much an advocate for, ‘How can we help the young children?’”
Following his performance at Buckingham Palace, David tweeted: “An honour to play for Her Majesty The Queen for her 70th Jubilee celebration weekend at Buckingham Palace. Thank you for all the love pouring in for my TS5 performance. Appreciate and love you.”
Last month, the singer released a song encouraging people to travel by train to be more environmentally friendly.
The song, titled “Better Days (I Came By Train)” was released on 26 October with an animated video by Golden Wolf studio and is part of a wider campaign by Thetrainline.com.