According to Vanity Fair, the royal trio will be guests at the wedding in September and although few specific details are known about the ceremony, it's believed it will be a lavish affair.
Charlie, who was once romantically linked to Kate's sister Pippa Middleton, knows the Princes from their days at Eton.
William, Kate and Harry are expected at the Italian wedding in September
The groom owns several London restaurants and nightclubs and is the man behind venues including Bunga Bunga and Mr Fogg's, while his wife-to-be Anneke von Trotha Taylor works in PR.
The couple are said to be well-known for their extravagant parties and Vanity Fair also reports that the Duke and Duchess of Cambridge have asked Kate's parents Michael and Carole Middleton to look after Prince George while they let their hair down at the Italian nuptials.
Charlie and Anneke have been together for four years
Charlie and Anneke got engaged in August 2013, having dated for three years.
William, Kate and Harry unveil poppy tribute to fallen World War I heroes
The 30-year-old is believed to have popped the question to his girlfriend while on holiday at the five-star Masseria Torre Maizza hotel in Puglia and using on a message placed inside a specially crafted fortune cookie.
Charlie and Anneke are close to the Middleton family and joined them at the river pageant during the Diamond Jubilee celebrations in 2012
William, Kate and Harry regularly attend both public and private events together.
In the past few months they have made official appearances at the Tower of London, the Tour de France and the Commonwealth Games and in March they stepped out as a trio for Lucy Meade and Charlie Budgett's wedding in Wiltshire.