Kate Middleton is spending her second day at King Edward VII Hospital in London after she was admitted following the announcement that she was pregnant and she may have to stay there at least several more days.
The Clarence House confirmed to ABC News Kate will be in the hospital for "several days," and will then require a "period of rest" battling severe morning sickness.
Prince William has been the only member of the royal family seen visiting Kate in the hospital. William departed the hospital Monday night around 8 p.m. before arriving again this morning to be at his wife's bedside.
A palace source tells ABC News that the royal couple decided to go public with the pregnancy because Kate had to be hospitalized.
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"Well they didn't want to let it out because she's still probably about the 10- week mark but they knew that once Kate was seen going into the hospital… that it was going to be out of their hands and then the media would have control of the announcement," Ingrid Seward, editor-in-chief of Majesty magazine, told "Good Morning America."
William and Kate were spending time with her parents in Bucklebury when she became ill with the symptoms of hyperemesis gravidarum, or acute nausea.
Prince William sprung into action and drove his wife along with their personal security team 50 miles in their Range River to the hospital where Kate was placed on an IV drip.
The royal family was only notified of Kate's pregnancy mere hours before the rest of the world.
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"They quickly told the queen, Prince Charles, Prince Harry and then they made the announcement at 4 o'clock yesterday," Seward told "GMA."
The announcement follows relentless public and media speculation about when Prince William and his wife would have an heir. The guessing game began almost immediately after the couple said, "I do" in April 2011.
It's customary for the royal couple to have a child within the first year of marriage. Princess Diana gave birth to William just 11 months after her wedding, and the queen gave birth to Prince Charles six days before her first wedding anniversary.
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Baby rumors went into overdrive after the Duchess of Cambridge toasted with a cup of water in September.
"Well, I don't know that she would have even known she was pregnant then. But it's possible, quite possible," Seward said.
Due to a dramatic change in the rules of succession, the royal couple's first-born will likely be the heir to the throne, regardless of the baby's gender.
Last year, the heads of 16 Commonwealth countries agreed to a change in the rules of succession so that first-born children of either gender can take the throne. Queen Elizabeth II was only eligible to be monarch because her father had no male children. The British Parliament must still amend existing law to make the succession change official.
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Many are speculating that Kate could be pregnant with twins because she is stricken with the condition hyperemesis gravidarum, which experts say is sometimes associated with having twins.
What does that mean for the hierarchy and the future of the throne?
"Well it would really be a case of which child appeared first," Seward said. "Whether it's male or female, the firstborn will be in line to the throne. It's that simple."
ABC News' Christina Ng and Sydney Lupkin contributed to this report.