"If the reports that were published … on the treason in the making and the intentional double language, is true - and it has not been contradicted - then it is a major breach of confidence and a very bad signal", the ambassador told The Sydney Morning Herald and The Age newspapers prior to being recalled to France.
Thebault cited "very reliable reports from the independent press" as saying that AUKUS was "in the making for 18 months".
"Which means we have been blind-sided intentionally for 18 months... The crime was prepared for 18 months", he added.
Thebault said that during these 18 months, there were "no warnings whatsoever" from the Australian side on its intention to unilaterally abandon the deal. Furthermore, it was not until after the reports that Australian Defence Minister Peter Dutton contacted his French counterpart, Florence Parly, to inform her of Australia's decision, the ambassador said.
A Rivercat ferry passes by the Royal Australian Navy's newest Collins class submarine, HMAS Waller
© REUTERS / David Gray/Files
He stressed that by ditching its deal with Paris, Canberra has made a "huge" diplomatic error.
"I would like to run into a time machine, if possible, and be in a situation where we don't end up in such an incredible, clumsy, inadequate un-Australian situation," Thebault said. "I'm very sad to be forced to leave, albeit there needs to be some reassessment to be made".
The diplomat expressed such criticism after on Wednesday, Australia, the United Kingdom and the United States announced a defence partnership, dubbed AUKUS, wherein Washington and London will supply Canberra with nuclear-propelled submarines. Australia quit a $66 billion deal with France, which was supposed to supply it with 12 conventionally powered submarines.
In an unprecedented move, Paris recalled its ambassadors from the United States and Australia for consultations. French Foreign Minister Jean-Yves Le Drian described Canberra's abandoning of the commitments before Paris for the sake of a trilateral pact with London and Washington as "stabbing in the back."