Grimmer fronted Wollongong Local Court on Wednesday morning where he was committed to stand trial on two counts of attempted aggravated sexual assault and one count of aggravated sexual assault.

The charges stem from allegations Grimmer molested the 30-year-old woman on several occasions between 2016 and 2018.

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A subsequent report to police in September 2018 prompted an investigation by detectives attached to Wollongong police.

Grimmer was arrested in January during an early morning raid on his Mount St Thomas home and taken to Wollongong Police Station, where he was charged and remanded in custody.

The 55-year-old chose not to appear in court late that day or apply for bail and has remained behind bars ever since.

Grimmer, along with his brothers Ricki Nash and Paul Grimmer, have spent decades trying to unearth what happened to their three-year-old sister Cheryl, who disappeared from Fairy Meadow Beach in January 1970.

Police suspect Cheryl was kidnapped and murdered but the case remains unsolved to this day.

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A Victorian man was arrested in March 2017 and charged with Cheryl's murder, however the case against him was dropped in 2019 after key evidence was ruled inadmissible for use in court.

Grimmer's January arrest came just weeks after police announced a $1 million reward for any members of the public who came forward with information that could lead to the arrest and conviction of Cheryl's killer.

There is no suggestion Grimmer himself was responsible for his sister's disappearance - he was only six years old at the time.

Grimmer will face Wollongong District Court next month for arraignment on the charges.