I agree with Sophea in that it's unlikely your inheritance would be considered part of the joint asset pool. Even though property settlements are decided based on the financial circumstances relevant on the day of hearing (as opposed to on the day of separation), only assets in which both parties have a shared interest form part of the asset pool. I can't imagine your inheritance would be considered a joint asset because your former party would not have benefited from it or contributed to it in any way.
In regards to mediation, there will be no repercussions for you if you don't disclose the inheritance during family dispute resolution. All matters discussed there are confidential (bar the obvious exceptions, like disclosure of child abuse, etc.), so they have little bearing on any court proceedings that may follow.
If it does end up court, though, you are obliged to make full and frank disclosure, as Sophea said, but it's just as likely as not that the court would determine that the inheritance be excluded from the asset pool.