The 'secret' debut of the Ducati Desmosedici GP12 MotoGP machine took place at Jerez on Tuesday, during the start of a three-day private test.

No pictures or official information have been released from the test, the first for a bike described as '90% new' by Ducati Corse general manager Filippo Preziosi.

That machine - absent from last week's Wrooom press event - is being tested at Jerez alongside the previous version, as used by Valentino Rossi in November's post-race Valencia test.

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Both types of bike are then due to be handed to Rossi and factory team-mate Nicky Hayden for the start of the Sepang MotoGP test, on January 31.

Ducati's reigning World Superbike champion and former MotoGP star Carlos Checa, plus development rider Franco Battaini (also a former grand prix rider) are carrying out testing duties at Jerez.

Following Tuesday's debut, Checa wrote the following brief message on his @CarlosCheca7 Twitter account: "1st test this year recovering good feelings on bike, we are working well. I can't say so much, tomorrow more work. Ciaoo!"

One of Rossi's mechanics, Alex Briggs, has emphasised the amount of work that has gone in to the 'new' Desmosedici.

Writing on @Alex__Briggs, he said: "The test in Jerez is a major check and to get a base setting, for everything. The bike we [assembled in Bologna recently] is NEW.

"This sort of thing would normally have been built & testing started about June [last year]. It's major!

"Ducati have done an awesome job in the time since the Valencia test. The factory has been flat out & it's not over yet."

The GP12 will be the first Ducati MotoGP bike to feature a twin-spar aluminium frame. MotoGP engine size is also increasing from 800cc to 1000cc for the 2012 season.

Seven time MotoGP champion Rossi and 2006 champion Hayden finished seventh and eighth in the 2011 standings, with one podium each.

Checa, Spain's first World Superbike champion, will stay in WSBK to try and defend his crown in 2012.