The Hills star's dad, Bill Montag, was arrested in January (15) for allegedly committing acts of sexual abuse on a teenage family friend between the ages of 13 and 17.

The unidentified girl claims she was given "back rubs in her bedroom" by the accused, who allegedly performed a sex act on her when she was just 16.

The alleged incidents occurred more than 15 years ago.

Bill's attorney, Forrest W. Lewis, tells Us Weekly his client pleaded not guilty to the charges, and the case is now set for trial.

Sources close to Heidi previously told the publication the accuser is "determined to destroy the family" and the former The Hills star is convinced her dad will be exonerated.

Bill walked Heidi down the aisle before she exchanged vows with Spencer Pratt on TV in 2009.