But now we hear there's a fly in the ointment - in the shape of Cheryl Cole.
Sources close to Derek, 27, and Katherine, 32, tell us the singer's upset with Derek putting Chezza first.
'She feels Cheryl has too much influence over him,' says a friend.
'Cheryl called him recently when he was out with Katherine and he spent ages on the phone.
'It's normal for them, but Katherine felt like a third wheel.'
Despite strong denials by Katherine's representatives, Now's source adds: 'Cheryl's a good friend of Derek's, but it's becoming a sticking point for Katherine.
'Every girl wants to feel they're most important.'
But a source close to Cheryl, 29, says: 'Cheryl isn't aware of how Katherine feels and she'd be mortified that she's put Derek in that situation.'
See our hot shot of Derek Hough in Now magainze dated 30 July 2012 - out now!
PICTURES Derek Hough's story in photos>>
