Sources say that the Dancing With The Stars celeb has been referring to the Vampire Diaries actress as "his girlfriend".
"[Nina] was hanging a lot with Derek's sister Julianne. Then she fell for him," an insider revealed.
And it seems he returns her affections. "Derek is smitten with Nina," the insider explained. "He said he hasn't felt this way for a girl in a long time."
A spokesman for Derek Hough has refused to comment on the new developments.
Nina has most recently been dating her Vampire Diaries co-star Ian Somerhalder, who she was with for three years, before they split in May. The actress admitted she likes to have a boyfriend, saying at the time: "I've been a relationship girl and I've been in long-term relationships my whole life until this point."
Derek, meanwhile, has previously been linked to Cheryl Cole following her split from husband Ashley, Shannon Elizabeth and The Hills Lauren Conrad.
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