A PANICKED Prince William has called in top doctors to help save his pregnant wife Kate Middleton and their unborn child – as the Duchess of Cambridge’s weight plummets to an alarmingly thin 91 pounds!

Following Kensington Palace’s Sept. 8 announcement that she and William are expecting their second child, royal sources have disclosed a bombshell secret, 
The National ENQUIRER has learned exclusively.

“William is terrified – not only for his wife – but also for the fate of his unborn child,” a palace insider said.

The ENQUIRER can reveal pregnant Kate, 32, looked painfully thin on Sept. 4, the last time she stepped out publicly before needing medical treatment.

On a rare romantic outing with her husband to a remote pub in England, Kate’s baby bump was barely noticeable, as these world exclusive photos show.

An onlooker at the restaurant told The ENQUIRER: “You really had to look to find the bump.” Inside the pub, Kate barely ate, the spy added.

“They both ordered fish with roasted vegetables on a bed of spinach. Afterward, she and William shared a single vanilla ice cream scoop, eating with two spoons from the same bowl. She didn’t even order her own dessert.”

Kate, 32, casually dressed with her skinny jeans glued to her barely-there waistline, covered up the tiny bump with her left hand as she left the venue. Just days later, doctors treated Kate at her home for the same debilitating form of morning sickness she endured while pregnant with first child Prince George in Dec. 2012, known as hyperemesis gravidarum.

While news of the pregnancy was a cause for celebration around the world, Behind the scenes, news of the pregnancy has placed a strain on William and Kate’s marriage, The ENQUIRER has been told.

The Duke of Cambridge, 32, called in top royal doctors to tend to his wife, ordering them has ordered doctors to place Kate under their 24-hour care.

“Kate has been vomiting up to 30 times a day and she’s been starving herself, which means she’s starving her baby,” the source said.

“Despite the efforts of their immediate family, Kate’s simply refusing to eat and that’s leading to the fears.”

Dr. Arthur Wisot, M.D.,  warned that Kate’s physicians “may even need to insert a feeding tube to ensure that she gets vital nutrients.”

The noted gynecologist and reproductive expert from L.A. told The ENQUIRER that Kate’s medical condition and her “inability to eat” could lead to doctors “forcing her IV fluids” or even using “hyperalimentation or a feeding tube to supply her body with electrolytes and vital nutrients.” The ENQUIRER has learned Kate’s dramatic health crisis could have even more dire consequences – both for her and her unborn BABIES!

Revealed a palace tattletale: “While the official announcement said Kate was expecting another little prince or princess, it’s possible she’s actually carrying twins.

“That’s because an ultrasound test performed around the six-week mark of her pregnancy indicated the presence of two heartbeats!”

Said Dr. Wisot: “If she is pregnant with twins, this may make her nausea more severe. The major danger of carrying twins is premature delivery. Other possible complications include hypertension and pre-eclampsia.”

While the royals have been silent on rumors of twins, beyond saying Kate is not yet at the 12-week mark, The ENQUIRER has learned that the couple have genetics on their side for a multiple pregnancy.

William’s maternal uncle Charles Spencer – brother of his mother, the late Princess Diana – has identical twin daughters. Diana’s grandfather, Lord Fermoy, was also an identical twin. Kate’s paternal grandmother had a twin sister and her father, Michael, had twin great aunts, also.

The insider added: “William should be over the moon, but he can’t help but be in fear over Kate’s condition. Everyone is praying she’ll pull herself together.”