The American Idol judge, 44, and Chmerkovskiy, a 34-year-old Dancing with the Stars pro, were very "affectionate" during an outing at Greek restaurant and lounge Nammos Estiatorio in Southhampton on Thursday, E! News reported.
Although Chmerkovskiy didn't arrive to Lopez's bash until around 1AM, an insider told E! News, "They seemed really happy to see each other."
"Jennifer was the last to get there, she came with her sisters," the insider said. "She looked amazing in a white crop bustier underneath a white pantsuit. She was glowing."
After dinner was served on the patio and Lopez blew out the candles on her cake, everyone reportedly hit the dance floor.
"No one danced more than Jennifer," a source added. "She barely sat down all night! Of course, the DJ played some of her hits. She was really tearing it up, dancing until the very end."
Lopez dumped backup dancer-turned-choreographer Casper Smart, 27, earlier this year in an "amicable process," according to an Us Weekly source.
Rumors have since been circulating Lopez may be dating Chmerkovskiy. Sources have claimed they kept in touch after Chmerkovskiy performed with her at the American Music Awards last November. The couple reportedly met through Remini, Lopez's best friend, who had competed on Season 17 of Dancing with the Stars and hopes the two performers will date.
"No I'm not. #rumors #nottrue," Lopez wrote, further clarifying things in her second post.
"No I'm not. (dating anyone new already.)," she tweeted at the time.
FOLLOW REALITY TV WORLD ON THE ALL-NEW GOOGLE NEWS!
Reality TV World is now available on the all-new Google News app and website. Click here to visit our Google News page, and then click FOLLOW to add us as a news source!
Chmerkovskiy has apparently been single since his last relationship with Sports Illustrated supermodel Kate Uptonended in December although reports had circulated for weeks he was dating his Season 18 Dancing with the Stars partner Meryl Davis. Both dancers repeatedly insisted there was nothing romantic going on between them.