The new parents left their baby son George at home with a sitter - no doubt Kate's mum Carol - before heading to the Tusk Conservation Awards in London.
The glittering dinner was held by the Tusk Trust, which aims to protect wildlife, communities and improve education in Africa, and the Duke and Duchess of Cambridge were the guests of honour.
Kate proved her yummy mummy credentials by wowing in a sparkling silver dress. The gown flattered her slender post-pregnancy figure and she teamed it with silver heels and a simple silver bracelet.
The mum-of-one wore her hair loose and topped off her look with smoky eye make-up.
Prince William, meanwhile, looked dapper in a tradition black tuxedo and dickie bow and stood close to his wife as they talked to fellow guests.
Kate gave birth to her first child, George Alexander Louis, at St. Mary's Hospital in Paddington, London on 22 July.
This was supposed to be her first public engagement following Prince George's birth, however she surprised everyone by attending the Ring O' Fire Anglesey Coastal Ultra Marathon on 30 August.
We saw the royal baby the day after the birth when she posed with William and their newborn outside the Lido Wing, and again the following day when the new parents were snapped taking little George to Kate's parents' home in Bucklebury, Berkshire.
Weeks later, Kate and William released the first pictures of George since the hospital photocall, choosing to use intimate family pictures taken by Kate's dad Michael Middleton rather than a professional photographer.
Speaking about his son, William recently said: "He's a little bit of a rascal, put it that way. So he either reminds me of my brother or me when I was younger!"
Check out the first pictures of Kate, William and George leaving the hospital below: