It was on May 17, 2008, that then Autumn Kelly married Peter Phillips, the eldest grandchild of Queen Elizabeth II and Prince Philip, at St. George's Chapel at Windsor Castle. Canadian Autumn chose to wear English designer Sassi Holford's design for her wedding gown, which featured a two-yard train. It was made of Chantilly lace and Italian duchesse satin. The lace ensured that her shoulders were covered, inkeeping with royal tradition. She wore the Festoon Tiara loaned to her by The Princess Royal.

The wedding appeared to have both British and Canadian/American traditions. For example, Autumn had older bridesmaids who wore different colored dresses than the bride; in British royal weddngs, bridesmaids tend to be younger and wear dresses in similar colors to the bride.

Autumn had six bridesmaids including Zara Tindall (nee Phillips) and Stephanie Phillips, Peter's sisters. Stephanie is Captain Mark Phillips's daughter from his second marriage. They wore green strapless dresses by American designer, Vera Wang.

Raised in the English-speaking West Island region of Montreal, Quebec, Autumn converted from Roman Catholicism to Anglicanism before her wedding so that Peter could remain in line to the British throne. She did retain her Canadian citizenship. 

The wedding caused a bit of controversy after Peter and Autumn sold photos of their wedding exclusively to Hello! Magazine and granted them an interview before the wedding. They were reportedly paid half a million pounds for the spread. The magazine published 59 pages of photos from the wedding. This decision angered some MPs, who called in to question the role of minor royals, and it is not believed the Queen was asked for permission before they agreed with the magazine. 

Their reception was held at Frogmore House. 

They have two daughters: Savannah (b. December 29, 2010) and Isla (b. March 29, 2012). Due to Autumn retaining her Canadian citizenship, both Savannah and Isla are dual Canadian/UK citizens - making them the first and closest Canadians to the throne.