There was something old and something new in the ring Meghan Markle, the American actress, wore when she and Prince Harry announced their engagement on Monday.

The ring, which the prince himself designed, bore three glittering diamonds: a central stone from Botswana and two others from the collection of the prince’s mother, Princess Diana, who died in 1997, the couple said in a joint interview shared on social media on Monday.

“It’s incredibly special to be able to have this, which sort of links where you come from and Botswana, which is important to us, and it’s perfect,” Ms. Markle said to Prince Harry during the interview. The ring is yellow gold, Ms. Markle’s favorite, Prince Harry said.