Pregnant Kate Middleton is staying home to take care of her own "precious" in-the-making.

Bearing with a second bout of acute morning sickness -- a rare condition known as Hyperemesis Gravidarum -- the royal mom-to-be has canceled a planned red carpet appearance at the London premiere of The Hobbit on Wednesday Dec. 12.

"The Duchess of Cambridge will not attend The Hobbit Premiere tomorrow evening and will continue to rest privately," a St. James Palace rep tells Us Weekly. In her stead, however, "the Duke of Cambridge will attend as planned."

Although the Duchess, 30, left King Edward VII hospital on Thursday after four days of treatment, she fell ill again over the weekend, and has been laying low at the Nottingham Cottage residence she and Prince William**, 30, share at Kensington Palace.

"Until further notice, to allow the Duchess a degree of privacy during her pregnancy, we do not intend to offer regular condition checks or advise of routine developments," the Palace told Us on Monday.

Keeping a commitment to attend a Dec. 8 Winter Whites Gala at London's Royal Albert Hall, William commented on his wife's struggles.

I don't know why they call it morning sickness -- they should call it all day and all night sickness," the prince joked. "[Recovery is] a long old process but she is getting there. She feels like it is going to go on forever."

This article originally appeared on Usmagazine.com: Pregnant Kate Middleton Cancels Red Carpet Appearance at London Hobbit Premiere to "Rest Privately"