Demi Lovato and Mike Johnson were too ''busy'' to make their romance work.

The 'Sorry Not Sorry' hitmaker enjoyed a string of dates with the 'Bachelorette' star last month, but were rumoured to have called time on their relationship earlier this month when it was said love between them had ''fizzled out''.

And now, sources say the couple - who were ''never serious'' in their romance - decided to go their separate ways because of their conflicting schedules.

Speaking to Us Weekly magazine, a source said: ''Mike and Demi have pumped the brakes. They went on a couple of dates and texted each other every day, but it was never a serious, full-blown relationship by any means. There is absolutely no love lost between them. The timing just wasn't right because they're both so busy.''

It was previously claimed Demi, 27, and Mike's romance had ''run its course'', but sources believed Mike was hopeful of a second chance in the future.

Another insider said: ''Demi and Mike's fling has fizzled out and they aren't seeing each other or texting like they were before. Nothing happened, it just ran its course.

''Demi was definitely interested in Mike at one point, but it was short-lived and she wasn't ever planning on dating him seriously.

''Mike hopes they can have a second chance again. But for now, he's fine with being friendly.''

The couple began dating after Mike appeared on 'The Bachelorette', where he was trying to win the heart of Hanna Brown.

Demi watched the show and confessed her love for Mike on social media, and the portfolio manager liked the fact she was the ''aggressor'' who made the first move in their budding romance.

He said: ''For one, I'm all about her too and she definitely was the aggressor. I find it incredibly sexy. I love that.

''Like, you want me, come at me. If I want you, I'm going to come at you - and I'm coming at her as well.''