Miley Cyrus and Selena Gomez's latest feud reportedly began at their mutual pal's birthday party.

Are Miley Cyrus & Selena Gomez Dissing Each Other On Social Media?

Cyrus and Gomez are both friends with Cody Simpson and he recently turned 18 on Jan. 11 and celebrated with a bunch of his young Hollywood friends.

Cyrus' boyfriend Patrick Schwarzenegger even snapped a photo of the Aussie blowing out candles on his birthday cakes, which he posted on Twitter.

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Cyrus and Gomez appear to be dissing each other as of the last few weeks on social media.

Cyrus mocked Gomez and then mocked her some more and Gomez only recently fired back on Jan. 24 with the help of her friend and fellow actor Brandon Smith.

Hollywood Life reported Tuesday that Simpson's birthday party is what initiated the social media fueled feud between the two 22-year-old stars.

A source revealed Cyrus and Gomez were anything but nice to each other at Simpson's party.

"Miley and Selena got at it at Cody's birthday party," the source shared, adding, "Miley said something about Cody having to have two different birthday parties in order to cater to Selena who didn't want to have any run-ins with Justin."

Cyrus' apparent comment irked Gomez even though the source said the Come & Get It singer tried to ignore Cyrus.

The source added, "By the end of the night, word got back to Miley that Selena thought she was always trying to be the center of attention," since Gomez reportedly thought Cyrus bringing up her ex was to rouse drama.

"Selena just thought it was uncool of Miley to be in her business and to talk about Justin at Cody's party. She felt like Miley was just trying to stir things up. She feels like Miley has always had a grudge against her since they were kids and thinks it's immature and mean," the source stated.

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Miley Cyrus, Selena Gomez