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These vamps are shacking up! Us Weekly has exclusively learned that Ian Somerhalder and Nikki Reed are already living together -- and they took the next step just three weeks after they began dating!

PHOTOS: Ian and Nina -- the way they were

An insider reveals to Us that the couple's new address is in none other than Atlanta, Ga., where Somerhalder is currently filming season six of "The Vampire Diaries" with his costar and (amicable!) ex-girlfriend Nina Dobrev.

PHOTOS: TV and movie vamps through the years

"[Nikki] goes to set every day," the source says, adding that the lovebirds plan to also share an L.A. place, too.

Sleeping under the same roof is the second big milestone in the pair's relationship. Two weeks after Us broke news that they were an item, Somerhalder revealed that he and the "Twilight" alum, 26, were the proud new owners of a horse named Eagle.

PHOTOS: Celebrities riding horses!

"What amazing creatures they are. Wow," Somerhalder, 35, wrote via Instagram on Aug. 5. "Thank you @iamnikkireed for snapping this special moment, with our big baby boy."

Somerhalder previously dated Dobrev for three years until their split in May 2013. Reed filed for divorce from husband Paul McDonald after two years of marriage in May 2014, and briefly dated Dancing With the Stars pro Derek Hough (also Dobrev's ex) before falling for the TVD hunk. Friends of the couple, however, don't seem shocked about how serious it's become between the two.

PHOTOS: Celeb couples -- how they first met

"There was always an attraction," a mutual pal explains to Us, "so it was easy to slip into dating."

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