Prince William visits Kate in the hospital as rumors swirl about royal twins

Prince William is back at the hospital today visiting his wife, Kate Middleton, who is there for the second day in a row with a pregnancy-related illness.

The Duke of Cambridge arrived at the King Edward VII hospital in London just before noon on Tuesday. Kate is there resting after being admitted with hyperemesis gravidarum, a condition characterized by acute morning sickness. 

PHOTOS: William visits Kate at hospital 

Though news of the illness may seem scary, it could actually indicate there may be royal twins on the way.

Dr. Manny Alvarez, senior managing health editor for, said Kate’s illness is more common with multiple babies.

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“The good news is that hyperemesis usually means a strong baby,” Alvarez said. “I have to wonder if she’s having twins.”

Related: Severe morning sickness linked to pre-term births

Their rep confirmed to Fox News on Monday that the couple, who married in April 2011, are expecting their first child.

"Their Royal Highnesses The Duke and Duchess of Cambridge are very pleased to announce that The Duchess of Cambridge is expecting a baby," the rep said in a statement. "The Queen, The Duke of Edinburgh, The Prince of Wales, The Duchess of Cornwall and Prince Harry and members of both families are delighted with the news."

The rep would not say how far along she is, only that she has not yet reached the 12-week mark.

"As the pregnancy is in its very early stages, Her Royal Highness is expected to stay in hospital for several days and will require a period of rest thereafter."

As the first-born to William — who is second in line for the throne after his father, Prince Charles — the couple's child stands an excellent chance of one day becoming monarch.

Whether boy or girl, the child will be next in line behind William in the line of succession to the throne, Cabinet Office officials have said.

The Associated Press contributed to this report.