Taylor Swift and Calvin Harris have split, and apparently, she was completely blindsided.

Although there have been many reports about the reason behind the split, both parties have remained silent, but a source claims Swift, 26, was convinced Harris was "the one" just before he ended their relationship after 15 months of dating.

"Taylor's completely torn apart over this," a source told Britain's Heat magazine, via Independent.ie. "She believed Calvin was 'The One.' This was it as far as she was concerned. She can't believe it's over."

Following a romantic getaway in March, which marked their one-year anniversary, Swift was sure that the 32-year-old DJ was about to propose.

"For Taylor, it came totally out of the blue when Calvin told her it was over and it wasn't working,” the insider added. “She's so heartbroken. She understands how difficult it is being with someone so high profile, but she thought he had a handle on it. But apparently not."

Swift and Harris parted ways at the end of last month just days after Harris was involved in a car accident in Beverly Hills, California, which forced him to canceled a couple of shows in Las Vegas.

"Calvin had been having doubts for months," a friend of Harris said. "His car accident two weeks ago really bought things to a head... It was after that he told Taylor it was over."

"Of course she's sad about the breakup, but she's leaning on her family and friends and looking forward," a Swift source added to PEOPLE Magazine last week. "She'll be just fine."

Just days after their split was confirmed, Swift attended a wedding and surprised guests with a special performance.

"There were lots of emotions entering [the wedding]," the guest explained. "Of course there was sadness as well, and Taylor was able to really transform that sadness into a celebration."

"Everyone at the wedding was blown away by the magic she was able to create," the guest continued. "We could never have dreamed that she would have responded to the letter in the way that she did. Taylor was unbelievably down-to-earth and normal."

Tags: Taylor Swift calvin harris