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Mellencamp arrived alone to the hotel first, an eyewitness tells ET, then was later joined by Brinkley. The two spent about an hour together, then left together in his chauffeured car. The "Jack & Diane" singer was affectionate towards her, touching the small of her back as he walked behind her, the eyewitness observed.

This is the first time the two have been seen out together, though they both attended the "Rock the Kasbah" special screening -- Bill Murray's new comedy debuting in October -- in New York late last month.

As for if this is indeed a new couple, a source tells ET, "It's not like that. This is the first time they've ever been out together."

The rocker's last reported relationship was with actress Meg Ryan, who he reportedly split with last August after three years together. After reconciling last October, the two broke it off for good a few months later, according to reports. Meanwhile, Brinkley's last public relationship was with her ex-husband, Peter Cook, who she divorced in 2008.

Last January, the still-gorgeous model opened up to ET's Nancy O'Dell about her dating life -- namely, how it was hard to date guys in her own age group. "It seems like during this period that most of the guys are like 38, 39, 42, like that sort of age group," Brinkley revealed. "It's funny because I think that at that age they have nothing to prove. They're very confident and do just what they want to do. [With] men my age I feel quite invisible to them."

"I think a ten year span is fine," she added.

WATCH: Christie Brinkley Gets a Black Eye Trying to Save a Bird

Check out Brinkley looking stunning in a white two-piece bikini during a family vacation to Italy in July, spending time with her three children, Alexa Ray, Jack, and Sailor.