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"I do," down under.

Mariah Carey has been engaged to billionaire James Packer for only week, but according to a new report, she's already eyeing an insanely-extravagant dress and a wedding near the Great Barrier Reef.

The Daily Mail says the two are planning to wed in a "huge private retreat" on Australia's Hayman Island.

"It's an absolutely stunning spot and they plan on using one of James' private planes to shuttle their guests in," a source said. "It will be an amazing party."

The source even said that designers are clamoring to design the diva's dress, including a 17-year-old fashion student named Sabrina DeSage who may have a leg up on the competition.

"Sabrina is an incredibly talented designer despite her age," a friend said. "She comes from a very well to-do family and her mother Debra knows James Packer socially. Mariah reached out last fall and made it clear that she has asked several designers to create a one of a kind design for her and that she will ultimately choose one of them."

The teenager obviously has an "in," but that's where it ends. "There's no guarantee that Sabrina's dress will be the one she wears on the big day, but it's a really exciting opportunity," the friend said.

Mariah, the report said, has already laid out plans for her dress. She wants to incorporate butterflies as the beautiful insect is often associated with the singer due to her well-received "Butterfly" album in 1997.

"That's her thing of course, and Sabrina's design has hundreds of gold butterflies, all sewn with 14-karat gold thread, flowing down the back of the silk gown and through the train," the Sabrina source said. "It's going to be absolutely stunning."

The dress could run upwards of half a million dollars, pocket change for James who proposed to Mariah with a 35-carat diamond sparkler. They're also renting out a home in Los Angeles that goes for $250,000 a month.

"Mariah knew she was going to marry him for some time," Daily Mail's source said.

The wedding, for now, will have to wait, as both James and Mariah are still legally married to their exes.