I honestly don't have an answer for that. I've read further that Mario was able to "charm" the Palace insiders to get an interview. I'm sure when he wrote that one sentence in his book and the media exploded, there was more than likely a purge of Palace insiders.
I read another article today stating that Paola knew that Delphine was Albert's daughter from the day she was born. If that is true, then either Albert confessed or Jacqueline told her or she knocked it out of Albert.