Royal watchers eagerly looking for signs of svelte Kate showing off her five month pregnancy were rewarded with the first distinct signs of a widening waistline.
Kate was attending the National Review of the Queen's Scouts for the first time in place of the Queen, who is celebrating her 87th birthday privately.
A volunteer in the Scout Association, Kate, 31, who is expecting her first baby in July, wore a short mint green Mulberry coat, fawn pill box hat and nude LK Bennett heels.
During the event, The Duchess of Cambridge talked to some of the 400-plus Queen's Scouts from around the UK and the Commonwealth.
The Queen's Scout award is achieved by carrying out regular community service for a year, learning new skills, completing a four day expedition in unknown terrain; taking part in a residential project and then sharing what has been learned with their peers.
The Duchess also met gallantry award holders, who have been nominated for their bravery and heroism and meeting adversity in their everyday lives.
Bear Grylls, Chief Scout of the Scout Association, paid tribute to the Duchess.
He said: "It's great that so many adults are joining the Scouts, and I am sure the increase has had much to do with the Duchess of Cambridge becoming a Scout volunteer last year.
"The Duchess is an incredible role model and she helps us show that Scouting's not just for boys.
"She's also such a generous volunteer and everyone is so excited to have her in the Scouting family. Many people have followed her lead and are getting involved and enjoying the adventure.
"They are huge inspirations to all the other Scouts across in the UK and I am so pleased that both the Duchess of Cambridge and Scouting have honoured them. Reaching Queen's Scout is a remarkable achievement and along the way they will have all had the adventure of a lifetime."