WATCH: Roger Federer's 'improved' boyband returns with Djokovic 'videobomb'

Remember Roger Federer's boyband? And the video of him singing alongside Grigor Dimitrov, Tommy Haas and musician David Foster which went viral during Australian Open? Well the tennis stars are back and one of their special friends make a guest appearance in this new video. 

Foster is again on the piano, as the trio belt out a rendition of the Chicago hit Hard to Say I'm Sorry. And the special guest is none other than Novak Djokovic. However, unlike the last video, this time the boyband took small amount of help from voice-enhancement tool, auto-tune and sounded a lot better than the last video.

This is the first video of the boyband