Rita Ora and Calvin Harris [Photo/Agencies]

The 'How We Do' singer and her boyfriend of nine months called time on their relationship this week and it's now been claimed that the Scottish DJ's reluctance to reveal details about his life before he met Rita was the cause of the split.

A source close to the couple told Yahoo! omg!: "The big issue was Calvin's secrecy and 'black book' which he refused to reveal to her.

"Calvin is very secretive and private and he keeps a black book which is all his private numbers, many of whom are girls. He refused to share this with Rita."

Rita, 23, and Calvin, 29, began dating last summer and looked to be music's perfect couple as they saw in the New Year together, but Rita - who will soon begin filming her role in 'Fifty Shades of Grey' - is reported to have been unable to accept his secretive behaviour which caused tension in their relationship.

The source said: "Rita introduced Calvin to her friends and colleagues but he refused to introduce her to anyone. She was this separate part of his life and he wouldn't include her in his work or social world.

"In the end they argued about it too much for him and he told her it was over."