Since her second birthday in 1979, Crown Princess Victoria's birthday has been celebrated as 'Victoria Day' in Sweden. Flags line the streets and wave from the buses, and the royal family fetes outside their summer residence, Solliden Palace, on Öland.
It will be the first time that Sofia Hellqvist, recently engaged to the Swedish prince, attends an event as an official member of the royal family.
Prince Carl Phillip and Sofia have been living together in Stockholm since 2011, and while she has attended royal events such as weddings and baptisms, she was not permitted to arrive with the royal family.
Victoria Day was originally conceived as an opportunity to give an award for major Swedish sporting achievements. Today, however, festivities go on for days, filling screens not just with the sport award but with races, the Victoria Fair, the Victoria Golf tournament, performances by famous Swedish artists, and much more.
This year the sports award goes to Sweden's two ski relay teams which competed in the Sochi Olympics. Performers at this year's festivities include Eurovision runner-up Sanna Nielsen, pop heartthrob Måns Zelmerlöw, Lill Lindförs, Alcazar, Panetoz, and Linnea Henriksson.
The celebration is "indispensable" for Öland's tourism industry. Shops on the island have longer hours and additional personnel during the festivities.