Kristian Herzog was fired by Grigorieva in October (10) after he was exposed as a convicted felon who had completed a jail term for firearms offences in March (10) - and was on probation.
Grigorieva only became aware of the security guard's criminal background when Gibson obtained a restraining order against Herzog, banning him from being around their baby daughter Lucia.
But Herzog, who was not made to sign a privacy agreement at the start of his employment, has since gone public with plans to release a book detailing claims he had an affair with Grigorieva following her split from the Hollywood actor. He has also alleged he's still in contact with the singer.
However, Grigorieva's attorney Daniel Horowitz has hit out at Herzog, insisting he's a "complete liar".
He adds, "(Herzog is) half blackmailer, and half psychopath."
And Grigorieva is adamant there is no truth to any of the reports, telling TMZ.com, "I don't speak to him. I don't communicate with him... I follow the court orders... He betrayed me."