The 27-year-old had been dating the Australian singer, 23, for just shy of a year following her split with husband Liam Hemsworth, and brief fling with Kaitlynn Carter.
Appearing on Instagram Live to discuss the break-up, the Midnight Sky singer told her 113 million followers that she wanted to “control my narrative” surrounding the events that led to the split.
“A year ago, almost to this exact date, the media tried to tell my story for me, and control my narrative, and I'm just not accepting that,” Cyrus told the camera.
“So today, it came out that me and my boyfriend have broken up.
"It was confirmed by a 'reliable source' even though no one is reliable in a relationship except the individuals who are participating in it.”
She added that the pair decided to part ways in order to “individually work on themselves.”
“But right now, two halves can't make a whole and we're individually just working on ourselves to become the people that we wanna be, like everybody else at this age.
“We are just deciding who we wanna be in our lives, what we wanna do, and so, don't make it some drama story if next week we're hanging out, getting pizza.
"We've been friends for 10 years and we're going to continue to be friends, so just don't make it something that it is not."
The pair’s friendship became closer five years ago, and blossomed into a romance ten months ago.
Sources told People last month that Cyrus has credited her recent sobriety to Simpson, who has regularly sung her praises.
“Being with Miley is a wonderful thing in my life,” he told The Sydney Morning Herald earlier this year.
Just days prior, Simpson said on his Instagram story that he was “in love with my best friend.”