WATCH: Kate Middleton says she's feeling 'broody' after meeting baby
The Duchess of Cambridge pulled out of the event "due to the children", according to PEOPLE magazine.
"The Duchess is no longer able to attend the Tusk awards due to the children," a spokesman for Kensington Palace told the publication. "She will still, however, meet finalists at a tea at Kensington Palace this afternoon. The Duke as patron will attend both."
Fans also hypothesised that the royal couple is expecting. One user tweeted, "This is quite odd, I hope nothing serious, just hoping Kate might be pregnant, that would be lovely!!!" while another put: "Maybe she’s pregnant and has that crippling morning sickness again?"
Fans are speculating over whether Prince William and Kate Middleton are expecting.
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It's unusual for Kate to miss a royal engagement and on the occasions she has, it has often been due to suffering severe morning sickness while pregnant.
For example, she had to miss Prince George's first day of school while battling with hyperemesis gravidarum when pregnant with Prince Louis in September 2017. When she was pregnant with Princess Charlotte, she was unable to attend several events for the same reason.
Amid mounting speculation the royal couple is expecting their fourth child, odds on William and Kate announcing a pregnancy towards the end of the year have been slashed. Bookmakers Ladbrokes currently have the Duchess of Cambridge at 4/1 to announce baby news before the year is over.