Things are getting serious between Mariah Carey and Bryan Tanaka!

A source close to Carey tells ET that the singer’s budding romance with her backup dancer -- which began after she split from fiance James Packer back in October and has been documented on her E! reality series, Mariah’s World -- is quickly becoming the real deal.

"She's into him now,” the source says, adding that Tanaka will be Carey’s “New Year’s kiss” after she performs in New York City on Dick Clark’s New Year’s Rockin’ Eve with Ryan Seacrest on Saturday. “He gets along really well with the twins.”

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The 46-year-old singer and her new beau spent the Christmas holiday together in Aspen, Colorado, with her 5-year-old twins, Monroe and Moroccan, and apparently, Tanaka also found some gifts under the tree from his new lady love.

"She bought him lavish designer Christmas gifts from the Aspen boutiques," the source adds.

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And while Carey is still wearing her 35-carat diamond engagement ring from Packer -- and, according to the source, plans to keep it -- the singer hasn’t been shy about showing her affection for her new man over the Aspen holiday.

"They walk around holding each other's hands and are always very affectionate. [They're] always smooching," an eyewitness told ET last week, adding that the couple, who are "clearly boyfriend and girlfriend" get along great and "like to cuddle."

See more about the pair’s getaway in the video below.

WATCH: Inside Mariah Carey and Boyfriend Bryan Tanaka's 'Romantic' Aspen Getaway