OKSANA GRIGORIEVA's bodyguard claims they've been having an "intimate" relationship since May.

Minder Kristian Herzog plans to release a tell-all book about his alleged relationship with the Russian singer - who has an 11-month-old daughter Lucia with her ex-partner Mel Gibson, who she split from in April this year - which will include details of their alleged relationship, as well as details of the legal battle ongoing between Mel and Oksana.

Gossip website TMZ reports: "Kristian Herzog - who was recently ordered to stay away from Lucia because of a criminal record involving guns - is telling people connected with the case he was Oksana's boyfriend for months and still communicates with her on a daily basis."

Mel and Oksana are currently embroiled in a bitter custody battle, with the Hollywood actor - who is believed to be worth $600 million -reportedly failing to keep up-to-date with his court-ordered child support payments.

The couple acrimoniously split amid allegations Mel assaulted Oksana during their year-long relationship.

Kristian is apparently claiming he has vital information about the case, and because he didn't sign a non-disclosure agreement before accepting the job, is prepared to tell all.

TMZ added: "Herzog is saying he has more than 1,000 text messages and more than 1,000 emails in which he communicates with Oksana about every detail of the case - Mel Gibson, evidence, witnesses, legal strategy and major conflicts between the players."