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Can't a guy just give a girl jewelry for no reason at all?

After many high-profile nights and days at the Cannes Film Festival, Diane Kruger and longtime beau Joshua Jackson hopped on over to Monte Carlo, Monaco, on Wednesday night.

At a Nights in Monaco benefit dinner and auction, the "Fringe" actor, 33, treated his girlfriend, 35, to a sweet treat, indeed: spending $45,000 on a Carla Amorim "Boreal" necklace, featuring 11.7 carats of white diamonds set in 18-karat rose gold.

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The "Inglourious Basterds" actress "was stunned" and "absolutely floored" by Jackson's over-the-top purchase, according to a witness. "She kept kissing him the rest of the night because she was so shocked still! The necklace is out of this world and he definitely had his eye out for it."

Still, despite rumors to the contrary, a source assures Us Weekly that the longtime couple, who've been dating for over five years, are not engaged.

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(Held at the Hotel de Paris, the inaugural Nights in Monaco auction benefited the Prince Albert II of Monaco Foundation and the William J. Clinton Foundation, and was also attended by Prince Albert II of Monaco, President Bill Clinton, Princess Caroline of Monaco, Rose McGowan, Billy Zane and others.)

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"Without sounding pessimistic, I learned that I don't believe in marriage," said Kruger to Glamour magazine in early February 2011. The star married French actor Guillaume Canet back in 2001, and they divorced five years later. "I believe in a commitment that you make in your heart. There's no paper that will make you stay. A guy friend of mine said, and it made a lot of sense, that people should get married at the end of the road, not the beginning."


The Couple at Cannes

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Diane Kruger's Glamorous Gowns at Cannes