The 'Star Girl' singer broke down in tears in front of bandmates and best men Harry Judd, Dougie Poynter and Danny Jones when tying the knot at London's One Marylebone on May 12.
Speaking about his sobbing at the altar, Fletcher explained: "I was doing okay up until that point, but hearing my sister sing and with Giovanna next to me looking so beautiful, I just lost it."
After the ceremony, Fletcher took to the stage with the rest of McFly for a 90-minute set, according to Ok.
The newlyweds also laid on a five-tier cake covered in Belgian chocolate roses and had their first dance to 'Easy' by The Commodores.
Fletcher's fellow McFly star Judd announced just five days after the ceremony his engagement to Escala violinist Izzy Johnston.
Watch McFly in the video for 'It's All About You' below: