The superstar DJ, who had been dating the singer and actress on/off for more than a year, took to the social media site last week to announce their relationship was over, but Rita was supposedly unaware he was going to release the message and still thought they could work through their issues.
An insider told The Sun newspaper: ''Rita was left embarrassed when he tweeted that it was all over.
''She didn't think he was going to make the announcement, so she was shocked.''
Last week Calvin wrote on Twitter: ''To address speculation -- myself and Rita ended our relationship some time ago. She is a beautiful, talented woman & I wish her all the best. (sic)''
The couple first split in January for a couple of weeks after a huge row but despite getting back together their hectic schedules meant they rarely saw each other.
Rita, 23, had also been seen partying and cosying up to other men in Instagram photographs and spent time been in Mexico with friends including the R&B singer Khalil Amir Sharieff, who was arrested in Miami with Justin Bieber earlier this year for drag racing.
The source said: ''It was Calvin's decision to end the relationship. They had been arguing for months and had grown apart.
''She was constantly posting snaps of her with other groups of friends and her trip to Mexico and photos of her with Khalil were the final straw.
''Calvin likes more privacy than Rita and he hated the extra attention that came with being her boyfriend.''
Since their break-up, Calvin, 30, has been spotted partying with a number of beautiful women and stars including Rosie Huntington-Whiteley in West Hollywood.
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