Catherine, Duchess of Cambridge, greeting guests at Clarence House, Oct. 26
Paul Burns/Clarence House/Getty
10/27/2011 at 10:15 AM EDT
With only 24 hours' notice, the Duchess of Cambridge
went to her first solo engagement in London Wednesday evening, stepping in for her father-in-law, Prince Charles.
Kate, 29, represented Charles, 62, at a dinner for the charity In Kind Direct
, because he was suddenly called to Riyadh to pay his respects to the Saudi Arabian Royal Family following the death of the Crown Prince.
"You would never know it was her first solo engagement. It was as if she had been trained by the Prince of Wales," the charity's chief executive Robin Boles tells PEOPLE. "She was completely natural, professional and charmed everyone. She spoke to every single guest and was genuinely interested, and interested in continuing to help."
"She said she had already called her mum to tell her about us in case Party Pieces [the family's children's party company] had surplus products."
Adds a Palace aide: "She was so pleased that her first solo engagement was for the Prince of Wales, who has shown her so much support over the years."
In Kind Direct was founded by Charles to encourage companies to donate surplus goods to charities, either for use by them or for their charitable work.
Guests at the dinner, held for 30 guests at Clarence House, were informed that Charles was sorry to miss the dinner but was sending his "darling daughter-in-law."