The 52-year-old royal and the South African Olympic swimmer, 32, will marry on July 2 in the Palace's Court of Honour.
The couple are keen to include the people of Monaco so palace gates will be left open and giant TV monitors set up to allow some 4,000 people to view the wedding service when it is held in the Place du Palais.
A palace spokesperson told People: “The religious ceremony will be held at 5 p.m. in the courtyard where we have the long staircase. It will be an open-air event."
A source added, "Whether the 4,000 will be invited guests or [members of the] public is still being discussed."
The pair will hold a civil ceremony – required by law – on July 1, in the Palace Throne Room, surrounded by 100 friends and family.
Monsignor Bernard Barsi, Archbishop of Monaco, will conduct the religious ceremony and Mass the following day
The nuptials will put an end to the playboy prince's bachelor lifestyle, as while he has never married, the royal has fathered two illegitimate children by two different women.
