It's been 60 years since Queen Elizabeth II took the throne, and the entire royal family is stepping out to celebrate. Prince William and Prince Harry attended The Diamond Jubilee River Pageant on The River Thames in London on Sunday, along with Duchess of Cambridge Kate Middleton, who wore a stunning red Alexander McQueen dress, accented with ivory-colored pumps and a Sylvia Fletcher hat.

William was decked out in his Flight Lieutenant No. 1 uniform, and Harry wore the ceremonial dress of the Blues and Royals. Middleton's entire family, including parents Michael and Carole, sister Pippa Middleton and brother James Middleton, were also in attendance, as were Prince Charles and Camilla, Duchess of Cornwall.

The weather didn't quite hold up for the event, but that didn't put a damper on the royals' attitude. "Kate was saying 'hi,' 'hello' to everyone she saw and was smiling ear-to-ear despite the bad weather," a source told Us Weekly. "William walked a step or two in front of her the whole time. She looked gorgeous in red — really slim and healthy looking."

For more on Kate Middleton, Prince William and the Diamond Jubilee:

Kate Middleton's Valentine's Day Charity Tour

Kate Middleton Accompanies Queen On Diamond Jubilee Tour In Leicester

Kate Middleton Takes Tea With Queen Elizabeth, Camilla For Inaugural Diamond Jubilee Event

Kate Middleton Flies Solo, William Away In The Falklands

Kate Middleton's Wedding Dress To Be Displayed