Los Angeles, March 7: Scottish DJ Calvin Harris has "politely declined" a collaboration with girlfriend Taylor Swift over fears that it would destroy their relationship. Harris, 32, doesn’t want to mix his professional with his personal life, a source told The Sun newspaper, reports dailymail.co.uk. It seems that Harris has learnt from his past as the mega-producer previously collaborated with ex-girlfriend Rita Ora on her last album before their sour split. “Calvin's next single is ready but the label is keen for him to get a big female US star to collaborate on it. They floated the idea of him working with Taylor but he politely declined it. Calvin has seen how sour things can turn when working with someone he's dating,” said the source. Harris has reportedly set his sights on working with Beyonce Knowles.