Mariah Carey has a brand new piece of jewelry -- a massive engagement ring -- 'cause her billionaire boyfriend James Packer just popped the question ... and Mariah said YESSSSS!!!!
It all went down in NYC -- where Packer secretly rounded up a bunch of Mariah's close friends for a private dinner at Eleven Madison Park ... so he could get down on one knee and propose in front of the most special people in her life.
Carey and Packer have only been dating since June 2015 -- but their relationship heated up real quick ... with the two famously spending several consecutive weeks together on his yacht over the summer.