Kate and William welcomed The President of the Republic of Singapore and Mrs Tony Tan Keng Yam on behalf of The Queen at the Royal Garden Hotel as part of the state visit to London.
The couple then travelled with The President and his wife to Horse Guards Parade.
The pregnant Duchess wore a grey Alexander McQueen coat and a Jane Taylor hat for the occasion.
Kate has not carried out any official engagements since she attended the Tower of London to see the poppy display on August 5.
BBC Royal reporter Peter Hunt said Kate was heard saying to The President: "I've been looking forward to getting out of the house."
Luckily she probably has a fair few rooms at 'the house' to keep life exciting.
Clarence House announced yesterday (October 20), that Kate is due to give birth in April – prompting speculating that she has recently had her 12 week scan.
The announcement also confirmed Kate was still suffering with hyperemesis gravidarum, but that her condition is 'steadily improving'.
The full statement read: "Their Royal Highnesses The Duke and Duchess of Cambridge are delighted to confirm they are expecting a baby in April 2015.
"The Duchess of Cambridge continues to be affected by hyperemesis gravidarum, but her condition is steadily improving."
Speaking about the betting odds, William Hill spokesman Rupert Adams said the flood of bets would normally mean there was truth in the rumours - but the announcement that the couple are expecting 'a baby' probably puts paid to all that.
Later the same day, Kate attended a black tie event at the National History Museum.
Kate chose a pale blue frock for the occasion, which sent the tabloids into a spin thanks to the amount of leg it showed off.
Kate was attending the Wildlife Photographer of the Year Awards alongside Sir David Attenborough, who looked dapper in a fancy tux.