"@ladygaga I acted like a child last night. Just not into publicity stunts call me & we will end this like adults I don't want 2 fight anymore," the Fashion Police star tweeted on Monday.
The apology came a little more than 24 hours after Kelly, who turned 28 on Sunday, expressed her annoyance over the fact that Gaga presented her mom, Sharon Osbourne, with a birthday cake in celebration of Kelly's big day during an appearance on U.K.'s X Factor.
"Not to be ungrateful but why would you send me a birthday cake via my MOTHER in a country half the would [sic] away? #JustSentItToME #LoveNotWar," Kelly wrote.
Kelly later posted an Instagram picture of what presumably was Gaga's cake with the caption, #EatMyS--t #Hypocrisy."
Not surprising, several of Gaga's fans soon came to her defense and proceeded to lash out at Kelly.
Later, the "Applause" singer briefly addressed the matter by simply tweeting, "Monsters, please just focus on the positive of tonight's performance and do not send any hateful messages. I don't support it. #SpreadLove."