The Duchess of Cambridge, née Kate Middleton, is expected to make a decision mid-week on whether she will travel to Malta for her first solo overseas tour later this month.
The mum of Prince George, who is suffering from hyperemesis gravidarum as she did with her first pregnancy, was due to represent the Queen on a two-day trip to mark the 50th anniversary of Malta's independence.
Kate was scheduled to visit on Saturday 20 to Sunday 21 September.
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When Clarence House announced that the Duchess was pregnant again, they also confirmed that while Kate and her husband Prince William were "very pleased" with the news, the Duchess would also be deciding her planned engagements on a "case by case" basis depending on her health.
Royal reporters have suggested that if Kate – who is keen to carry out the tour – is unable to travel, William may go in her place.
According to The Mirror, William's younger brother Prince Harry cancelled his 30th birthday party on Saturday night in light of Kate's illness, saying that he felt it was "inappropriate" to carry on with the celebrations.
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Prince Harry is said to have cancelled his 30th birthday party after Kate fell ill
Harry's mini banquet was meant to be held at William and Kate's newly refurbished apartment in Kensington Palace, but the fourth-in-line to the throne contacted guests saying he would have to postpone.
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"Kate had been very involved in organising Harry's party, and once she fell ill he felt it wrong to let the event go ahead," a source told the publication. "He has promised his friends he will organise a post-30th birthday party when the time is right."
Princesses Beatrice and Eugenie and Zara Tindall were all expected to attend their cousin's milestone birthday party, alongside William and Harry's good friend Guy Pelly.