Prince Charles' wife, Camilla, became a grandmother as her son's wife gave birth to a girl.
The Duchess of Cornwall's son, Tom Parker Bowles, and his wife, Sara Buys, have named their daughter Lola.
"The Duchess is absolutely thrilled," a spokeswoman for the prince's Clarence House office said on condition of anonymity in line with palace policy.
Parker Bowles, who is a food writer, and Buys, a fashion columnist, married in 2005.
Prince Charles is Parker Bowles' godfather as well as his stepfather.
On the second day of the St. Petersburg International Economic Forum, a plenary meeting was held, in which Russian President Vladimir Putin, French President Emmanuel Macron, Japanese Prime Minister Shinzo Abe, Chinese Vice President Wang Qishan and IMF head Christine Lagarde took part