Calvin Harris 'intimidated' by Taylor Swift

Taylor Swift and Calvin Harris amicably ended their 15 months old relationship. (Bang)

Calvin Harris reportedly broke up with Taylor Swift because he was "intimidated" by her success.

The 32-year-old DJ dumped the 26-year-old singer last week after 15 months of dating and friends believe it would take a "very secure man" to handle a relationship with her.

A source told PEOPLE: "Calvin said on multiple occasions that he was intimidated by Taylor, which is why he would not attend any events where she was being honoured, or any award shows unless he was nominated.

"Taylor is an independent young woman, and she knows it will take a very secure man to handle her success.

"It wasn't an equal relationship. Their age difference might not be significant for many couples, but for them it was part of the problem too. Taylor somewhat lacks real-life experience. They will not be getting back together."

However, the former couple plan to remain friends despite their split.

The source said: "She works incredibly hard for things that she believes in. He always saw that as an amazing quality. They are still friendly."

Meanwhile, it was claimed that Calvin - who recently had to cancel a number of shows after being involved in a car accident - had been "losing interest" in the 'Bad Blood' hitmaker for some time before they split.

A source told E! News: "Adam really liked Taylor, she was not the type of girl he ever dates and he liked that. He liked how innocent Taylor was and that she had a good caring heart. Taylor's heart was more in it then he was. He started to lose interest over the past few months, but really tried to not just break up."

And the couple's respective working schedules also didn't help their romance.

The source added: "They were just not very compatible in different areas in their relationship. The touring and traveling didn't help. It seemed like they were more friends than lovers.

"Taylor and Adam had very different group of friends."

Another heartbreak for Taylor Swift; splits from Calvin Harris

Taylor Swift and Calvin Harris have split up.

The 26-year-old singer and the 32-year-old DJ have ended their relationship of 15 months.

A source told PEOPLE: "There was no drama. Things just don't work out sometimes."

However, the split comes as a surprise as Taylor recently gushed about their "magical relationship".

She said in April: "I'm just taking things as they come.

"I'm in a magical relationship right now. And of course I want it to be ours, and low key...This is the one thing that's been mine about my personal life."

The musician, who previously dated stars including Jake Gyllenhaal, Harry Styles and Taylor Lautner, admitted the attention on her personal life put her off dating for a long time before she met Calvin.

She said: "You know, I went out on a normal amount of dates in my early 20s, and I got absolutely slaughtered for it.

"And it took a lot of hard work and altering my decision-making. I didn't date for two and a half years. Should I have had to do that? No."

Ellie Goulding originally set Calvin and Taylor up when she introduced them at the BRIT Awards afterparty in London in 2015.

She said: "How did I set up Taylor and Calvin? It just kind of happened.

"They're both good people, both dear friends. I thought it might work - and it did.

"Calvin is a really great mate and he's so fantastic, and Taylor is such a cool person who I love. I thought. 'They're both really awesome and both really tall, they'll brilliant together'."