Find out when the royal family -- including the Queen and Prince Charles plus the Duchess' mum Carole Middleton -- learned of Kate Middleton's second pregnancy. Credit: Anwar Hussein/WireImage

Mum's the word! Kate Middleton and Prince William, currently expecting their second child, kept her pregnancy a secret until very recently. A source tells Us Weekly that the Duke and Duchess of Cambridge only shared the news with the royal family this past weekend, before it was confirmed to the rest of the world.

"William and Kate told their parents the news this weekend," the insider tells Us of the couple, who told Prince Charles, Camilla Duchess of Cornwall, and Carole and Michael Middleton of their soon-to-be second grandchild.

The news was also shared with the matriarch of the royal family, one day before Kensington Palace released a formal statement. "The Queen and Prince Philip were given the good news on Sunday morning," the source says. "Everyone is delighted." Read William's reaction to the big news.

Another insider close to the couple told Us on Monday, Sept. 8, that William and Kate discovered they were expecting baby number two "very recently." The insider said the Duchess was approximately eight weeks along, and the parents of Prince George are "very happy, very excited."

As was the case with her first pregnancy, the Duchess has been experiencing acute morning sickness (hyperemesis gravidarum). She did not join Prince William on Monday, Sept. 8, at a planned royal engagement at St. Hugh's College as she was being treated at home by the Queen's gynecologist, Alan Farthing, and the royal household's gynecologist, Guy Thorpe-Beeston.

The Duchess' morning sickness, in fact, was what compelled the couple to make the "very difficult" decision to announce her pregnancy so early in the first trimester. "Their Royal Highnesses The Duke and Duchess of Cambridge are very pleased to announce that The Duchess of Cambridge is expecting their second child," the official Palace statement read. "The Queen and members of both families are delighted with the news."

An aide updated Us Weekly on Tuesday, Sept. 9, about the Duchess' health, saying not much has changed since the previous day. "The Duchess remains at her home in Kensington Palace and is being seen regularly by doctors who are treating her," the official said.