The 45-year-old proudly showed off her new yellow diamond heart necklace, thought to have set back Australian billion James over £320,000.
Mariah was clearly touched by 47-year-old James’ gift, as on Wednesday evening she dedicated a song to him during her performance at Caesars Palace Colosseum.
Before performing her hit Hero, Mariah gushed: “I have a new heart tonight. James is in my heart tonight.
On Saturday night Mariah attended Scott Disick’s night at Vegas club 1OAK and, while James was nowhere to be seen, she proudly displayed his gift.
It was reported this month that Mariah and James are already planning a baby – despite only getting together a couple of months ago.
An insider told Life & Style: “She wants another child and is telling friends she’s not too old.
"James is promising to spoil her throughout her pregnancy. He's convinced her he would not only be by her side 24/7, but he would hire round-the-clock care and the best doctors money can buy."
Meanwhile Scott, who recently split from Kourtney Kardashian after nine years, was at the club with a mystery blonde, who he was later accused of kissing.
But sources close to the reality TV star insist he wasn’t kissing the woman – he was innocently whispering in the waitress’ ear for some water.