The insiders also claimed that the two will remain best friends.
The Nickelodeon alum opened up about Miller, whom she first met in 2013 when they collaborated on the song "The Way", in Cosmopolitan magazine past year.
Grande has been on music hiatus following the bombing at her Manchester concert.
As for the reason for the split, the publication say Ariana and Mac "quietly cut off their romantic relationship" after their work schedules became "too busy".
"So proud of this girl right here", the "Senior Skip Day" rapper wrote.More news: A Fairly Nice Day, Even With Some Rain
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Speaking about his relationship with the 24-year-old during an interview on radio show "The Breakfast Club" in 2016, Mac called himself a "man in love", adding, "That is a true thing in my life, she's unbelievable".
In a candid interview with Cosmopolitan, she gushed: "I met [Mac] when I was 19". She is now currently working on her new album called Sweetener, which is scheduled to come out on July 20.
Singer Ariana Grande pulled out of 2018 Brit Awards at the last moment leaving organisers frantic.
The former couple were most recently spotted out together at Coachella, and before that at Madonna's Oscar after-party. She performed at a May 2017 concert in Manchester, England, where 22 were killed in a terrorist bomb attack. The two were together for two years.
Explaining why they didn't begin dating then, despite mutual adoration, she said: "We weren't ready at all, though, to be together". At least we know she's not crying over this breakup.