"Mariah wants a summer wedding and has set up meetings with event planners and designers.
"Mariah is telling everyone to expect the most incredible - and most expensive - wedding imaginable."
Despite it being her third trip down the aisle, Mariah - who has four-year-old twins Moroccan and Monroe with Nick - is convinced this marriage will last forever.
The source told Closer magazine: "Mariah is totally in love and James worships the ground she walks on - she credits him for bringing her back to life after her last divorce.
"She's joked he's the only man who can handle her. She has no doubts that this marriage will last forever."
- Bang! Showbiz