The Oscar winner, 33, was seen planting one on Horton over lunch in Studio City, Calif., this weekend. The singer has reportedly been dating Horton for several weeks.
A source told Entertainment Tonight that part of why Gaga is so happy with her new paramour is simply to shut everyone up about her chemistry with "A Star Is born" co-star Cooper.
"All the talk of Bradley was all in fun; she's ready to dispel those rumors once and for all," the source said, adding of Horton, "He is handsome and talented and she likes to date men on her team ... she is known as a workaholic, so it fits her lifestyle to meet someone while working."
"They're working very closely together at a home studio in Hollywood, and sparks just started flying," a source added. "People noticed the chemistry early on, and now that she has taken some time to herself, she finally feels free to date. They seem like a pretty good match."
Horton divorced Broadway actress Autumn Guzzardi in February 2018. Guzzardi appeared to reference his new relationship with the "Paparazzi" singer, posting a headshot on Instagram captioned "Poker Face."
A rep for Gaga did not immediately return a request for comment.