Mariah Carey 'Thrilled' With Weight Loss and Her 'Fresh Start,' Source Says (Exclusive)

ET's source says that opening up about her bipolar disorder diagnosis has been a 'huge relief' for the superstar.

Mariah Carey couldn't be happier with her fresh start in life -- starting with her weight loss. 

A source tells ET that the superstar is "thrilled" with her recent weight loss and is the happiest she's ever been. "She seems to be exuding happiness and she is," the source says. "She has had big changes in her life for the better. Both dropping her manager, Stella [Bulochnikov], and coming clean about her struggles with bipolar disorder have been a huge relief and it shows." 

Though Carey has never commented on her weight loss nor confirmed having weight loss surgery, ET learned in November that she had undergone gastric sleeve surgery. The 48-year-old singer split from her former manager the same month, and in April, she revealed that she was diagnosed with bipolar disorder in 2001. 

According to ET's source, Carey "needed a fresh start and she is getting just that."

"She truly feels her weight loss surgery paid off because she is at her happiest when she is thin," the source claims, adding that Carey, who is also dieting in preparation for her Las Vegas residency at The Colosseum at Caesars Palace, has worried her friends and family in the past about going "overboard" on her weight loss. 

“She has always struggled with her weight. In the last five years it has become more and more difficult for Mariah to shed the pounds," the source says. "She has a huge career, children, and she has been through big changes with her team. It's truly been an emotional roller coaster and that always affects her weight, both gain and loss." 

“Mariah is known for her yo-yo dieting. When she has a big project coming up, she works so hard to lose weight. She often becomes incredibly stressed out and barely eats. Then the moment her project is complete, she lets loose and enjoys all her favorite foods, champagne and the weight gain returns," the source claims. 

This time around, however, ET's source says Carey is doing things differently and is focused on staying healthy. "It has been hard for Mariah to get off the dieting roller coaster, but for now she seems very happy. She is focusing on new music and she is thrilled about her Vegas residency," the source says. "She often tells friends she wants to be the queen of Vegas and she seems to be on her way."

Carey certainly looks happy. The mother of two showed off her slimmed-down figure in a dazzling gown in New York City on Thursday, and has been flaunting her fit physique in several stunning looks over the last few months. See more in the video below. 

Reporting by Adriane Schwartz.