The "Poker Face" songstress went public with the audio engineer in July after the couple was seen sharing a smooch at a brunch. While Dan's identity was yet to be revealed, a source told PEOPLE magazine that Gaga and the mystery man seemed "very happy" together and had no qualms about sharing a kiss in front of dozens of bystanders.
News of their separation comes months after a source close to the singer claimed Gaga and Bradley Cooper were an item. After the pair secretly split, Gaga was reportedly telling her inner circle that The Hangover actor "broke her heart".
"There’s no doubt about it - Lady Gaga fell head over heels for Bradley during filming and promotion of A Star is Born," a source told Life & Style magazine. "She thought he was “the one” and assumed he felt the same way – until recently."
Although Bradley's alleged attitude spelled the end of their short-lived fling, with rumours swirling he "totally backed off", the unnamed source sensationally revealed that those closest to Gaga feared she was being "strung along" by the hunky A-lister.
"She’s telling friends he broke her heart. Gaga feels like Bradley led her on because he was giving off all the signs that they’d become an item once he was single," said the magazine's source, referring to Bradley's split from his girlfriend of five years, Irina Shayk. "He suddenly realised he was jumping into a full-blown commitment to someone else and got scared."
Bradley and his Victoria's Secret model ex-girlfriend sent shock waves through Hollywood when a representative confirmed in June that the couple had decided to call time on their romance.
An insider told PEOPLE magazine that they were "amicably working out how to share custody of their daughter Lea De Seine."
In the wake of their split, insiders claimed Gaga was reportedly the person Bradley went to for love and life advice.
"He goes to Gaga for advice over everything, which is pretty insensitive at a time like this but Bradley can’t help himself,” an insider told Radar Online a few months ago.
The source added: “He’s just totally spellbound by her and thinks she’s the wisest, coolest and most worldly person on the planet. Gaga’s in a tough spot because she doesn’t want to rub Irina’s nose in it. But still, she does adore Bradley so she’s happy to take his calls."