Meanwhile, although both Mariah and James are still legally wed to their estranged spouses, Nick Cannon and Erica Packer, she is already making plans for a huge ceremony in Europe this summer.
A source said: "Mariah is just beyond excited right now.
"She has wanted to be his wife pretty much since they first got together, and has already started to plan what type of wedding she wants to have.
"Mariah wants the wedding to be this coming summer and she said she would really love it if they could get married where they first fell in love, in the Mediterranean region.
"She wants this wedding to be the biggest and most expensive wedding that the world has ever seen!"
And friends of the 'Fantasy' singer - who has four-year-old twins Moroccan and Monroe with Nick - couldn't be happier about her engagement.
The source said: "All of her friends are really happy for her because when Mariah is happy, everyone around her is happy.
"She deserves a man who will treat her like gold and James does better than that. He treats her like platinum."
- Bang! Showbiz