Pauline Hanson has used parliamentary privilege to publicly place accusations on the ex-wife of her son, claiming she made false claims that he sexually abused his own child.

The One Nation leader’s surprising statement comes shortly after Prime Minister Scott Morrison appointed her as deputy chair of national enquiry in the family law system.

Earlier on Wednesday, Hanson said that it was her son’s experience with the system that motivated her to call for a royal commission into the matter.

She went into detail in July in the Senate, where she is protected by parliamentary privilege and cannot be sued for defamation.

“I know this feeling because, for years, my own son faced these destructive allegations in an attempt to stop him having access to his young son,” she said in July.

“My ex-daughter-in-law claimed to police that my son was outside her home in Townsville, which led to a DVO (domestic violence order) being taken out against him.

“That was despite him being sick and on the Gold Coast, some 1000 kilometres away. He was forced to defend himself, at enormous expense, and was dragged through the courts.

“She also falsely alleged – a soul-crushing claim – that my son had sexually abused this boy. Again, the false claim was designed to stop him having any connection with his son. No charges were brought against my son.”

Due to recounting this story in parliament, the senator is immune from laws that may have made it an offence to make details about family law matters public.