Singer Billie Eilish has spoken for the first time about her secret relationship and break-up with rapper Brandon Adams, known by his stage name 7:AMP.

The 19-year-old singer is the subject of Billie Eilish: The World's A Little Blurry, a new documentary on streaming service Apple TV+ released last week.

"I just wasn't happy. I didn't want the same things he wanted and I don't think that's fair for him," she said of Adams, 24, whom she called Q.

"I don't think you should be in a relationship super excited about things that the other person couldn't care less about."

At the start of the documentary, filmed over 140 days in 2018 and 2019, the two of them are seen to be in love but the cracks soon start to show in their relationship as she goes from viral sensation to bona fide pop star.

By the end of the 2½-hour documentary, the relationship is over.

While it is unclear when they had started dating, he first appeared in footage from her 16th birthday.

Though they never confirmed their relationship in public, Eilish had appeared on the cover of his debut album, Bleaupro, in February 2019, fuelling rumours of a romance at that time.

She also called it a life-changing album for her, listing it as a favourite.

They later broke up in the middle that year, not long after an incident in which he punched a wall and broke his hand, which she described as "self-destructive".

"There was just a lack of effort. I was literally like, 'Dude, you don't have enough love to love yourself so you can't love me, dude. And you don't. You think you do'," she said.

The single star had spoken on radio show Capitol Breakfast last September about her dating life.

"I mean, like, I've had relationships and kept them private. And even the ones that I've had, and like, the tiny amount that I've let the world see, I regret."

She added: "And it's like, what if it goes bad? And then everybody has this whole opinion on your relationship that they have no idea about. So it's very much not something I'm interested in."