David Bowie made his band sign gagging orders to keep his comeback a secret.
The musician announced a surprise return on his 66th birthday last week with new single 'Where Are We Now' and went to great measures to keep his return quiet.
Producer Tony Visconti, who worked on the project, told the Daily Mirror newspaper: ''The members of the band, the engineers, the people who bring us coffee - everybody involved had to sign a non-disclosure agreement (NDA).
''Most of the people had worked with David for a long time and signing an NDA would have been unnecessary normally.
''But we had some new people and a new recording studio, so we took the precaution. Everyone had to sign it. No one objected because they said it was a joy to be working with David Bowie.
''We kept it a secret on an honour system - it was cool to be part of this club.''
Guitarist Earl Slick has previously said he even had to be careful about where he smoked in between takes while recording for new album, 'The Next Day'.
He said: ''One day I went out to have a cigarette in front of the studio, and something felt weird. I would hang out in the doorway, in a little alcove; I didn't even walk into the street. And something felt weird, and I peered across the street, and there was a guy there with a camera on a tripod. So I put my cigarette out and went back inside. Because if they see me, they can put two and two together.''
Meanwhile Tony has said David may be open to performing a special one-off show in his hometown of London to mark his comeback.
He told the Daily Express newspaper: ''David's a London boy and London will be the location for the one-off open air show. Either Hyde Park or Wembley are the most likely venues.''
'The Next Day' will be released in March.