THE world is abuzz over news that Prince Wil­liam and Princess Kate are expecting – and The ENQUIRER can reveal that the Duchess of Cambridge is carrying TWO bundles of joy!

BUT, alarmingly, the royal twin pregnancy is already at risk because Kate’s weight has dropped to a frail 96 pounds, say sources in London.

And complicating the situation, Kate – who conceived the babies through in vitro fertilization – has been stricken with an acute case of morn­ing sickness called “hyperemesis gravi­darum” and is being moni­tored closely at a Lon­don hospital.

While Buckingham Palace has not con­firmed the fact that Kate is carrying twins, it has admitted that she’s facing a medical crisis.

“Kate’s weight has spiraled to a waif-thin 96 pounds, and if she doesn’t do something quick to stabilize it, doctors warn she’s go­ing to lose her babies,” the source told The ENQUIRER. “Kate and William are beside them­selves with fear over the health of the twins, especially after so many months of trying to get pregnant.”

The insider revealed that Kate and William secretly visited a top doctor and began IVF treatment in late July.

“They were ecstatic when they learned Kate was finally pregnant,” the source said. “But now their hap­piness is tainted by fear that the babies’ health could be at risk – or worse, that Kate could miscarry.”

Kate’s dramatic weight loss began before her April 2011 wedding to William and carried over into her married life, says the source.

“The stress of becoming a royal has been difficult for Kate, and it’s triggered a lot of serious issues with her weight,” said the insider.

“Her fast-paced lifestyle has af­fected her eating habits, and now she’s just a shadow of the girl she was only two or three years ago.”

The palace has confirmed that Kate, who turns 31 in January, is less than 12 weeks pregnant.

“Normally, all this would be kept secret, but the palace felt they had to release a statement because Kate had to go into the hospital,” ex­plained the insider. “There would have been endless speculation about what was wrong with her.”

Dr. Arthur Wisot, a noted gynecologist with Reproduc­tive Partners in Los Angeles, told The ENQUIRER that Kate’s babies could be in danger if she fails to gain enough weight during her pregnancy.

“If the babies do not get enough nutrients, they fail to thrive in the womb and could develop both short-term and long-term developmental problems, including neurological damage,” said Dr. Wisot. “The condition hy­peremesis gravidarum means liter­ally extreme vomiting during preg­nancy and only adds to the danger of her already thin and frail state.

“Some patients stay in the hospi­tal for months with this condition because they can’t keep any foods down.”

Dr. Wisot confirmed there’s also a chance of miscarriage.

“Obviously, Kate is getting the best possible medical treatment,” the source added. “Everyone is praying she and the babies will get through this OK.”