But before the pair's big role in the ceremony, which will take place on 20 May, we are taking a look back at their dad Prince William and uncle Prince Harry's own experiences as pageboys. Click through to see the adorable snaps of the young Princes wedding looks.
Prince William looked simply adorable in a sailor outfit, complete with a navy blue neckerchief and a matching straw hat, for the wedding of Prince Andrew and Sarah Ferguson in 1986. The little Prince pulled faces at a bridesmaid as they waited for the ceremony to start together.
Prince William looked a little bored while waiting for the bride to walk down the aisle, and hilariously hid his face using the string on his straw hat. Sitting on the edge of a lavish red velvet chair, he also showed off patent black shoes with white socks, completing the traditional look.
Prince William looked a little distracted while members of the congregation, including a fellow bridesmaid, stood up while holding songbooks. Holding onto his own booklet, the little Prince seems to be trying to get a better look at something else instead, good thing his bridesmaid friend looks like she is about to remind him to stand up!
Prince William laughed while he was being chased by Lady Davina Windsor outside Buckingham Palace. Lady Davina was also dressed up the nines in a cute light blue frock with matching shoes, and the rest of the guests made the royal children no mind as they enjoyed the special day.
In a rare moment of affection caught on camera, Queen Elizabeth II can be spotted with her arm around her young grandson while smiling for the camera, dressed in a pastel blue ensemble with a matching hat and shoes. The pair posed in from of the congregation, although Prince William looks ready to start playing again!
Prince William wore pink braces and a white and cream ensemble to match the bridesmaids while pageboy for the society wedding of Camilla Dunne to Rupert Soames at the Hereford cathedral. The second-in-line to the throne looked simply adorable as he smiled for the cameras.
The Prince looked like he was taking his pageboy duties in his stride as he put his hands in his pockets while surrounded by bridesmaids dressed in bold pink.
Prince William held his mum's, Diana, Princess of Wales, hand as they entered the church. Diana looked stylish in a royal blue ensemble, and waited patiently for her son as he gave a wave to the cameras before entering the church.
Prince Harry looked like he was taking his pageboy duties very seriously as he looked ahead in his cream suit with a burgundy velvet sash, complete with a wide brimmed hat. Holding a wicker basket, the Prince looked focused (much more focused than the little bridesmaid anyway!)
The little Prince was caught mid smile as he performed his pageboy duties at the wedding of Viscount Althorp and Victoria Lockwood.
Prince Harry held the hand of Diana's sister Lady Sarah McCorquodale as they walked to the wedding of Viscount Althorp and Victoria Lockwood. The little Prince was dressed in a costume inspired by Eighteenth-century inspiredby a painting which hangs at Althorp.