According to Us Weekly, the pair – who were first linked in April 2008, broke up and then made a splash at the 2009 Academy Awards together before splitting for a second time – are back on.
"He really got to her, and she's hooked on him," a source told the mag. "She just can't let go."
The source added that it was Mayer's magnetism that allegedly drew her back in, despite rumored summer romances with Gerard Butler and Bradley Cooper.
"There's something about John that she just can't resist," the source claimed .
And a Mayer source said that the singer-actress duo were "very close."
"They remain great friends. He thinks she's amazing, nice and smart, and he has nothing but respect for her," the source said.
According to the mag, the two rekindled their romance at the Four Seasons Hotel in New York City on September 22 and have been texting each other.
The singer, whose new album, "Battle Studies," is due in November, turns 32 on Friday, so perhaps Jennifer will help him turn a year older once more – in 2008, the two shared a night out at the Grand Havana Room in LA to celebrate his big day.
If the reports are true, John hasn't let on with his Twitter page, though the star did blast a different rumor on Thursday.
"Rumor check: went to gay bar in Palm Springs, yes. Had a blast. Danced my face off. Someone there planted a kiss on me? No," he Tweeted.
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