The pair will marry in the Church of Immaculate Conception at Rathfeigh in County Meath.
The reception will then be held in Slane Castle, where Westlife will perform a medley of their songs.
It will cost £100,000
The wedding will end with a huge fireworks display at 3am.
Guests lucky enough to be invited to the £100,000 event include stars such as Ronan Keating and S Club 7.