Undue influence as a reason for contesting a will

What is the name of your state? California

The arguement has been made that assumption of undue influence as a cause for contesting a will.
I found myself omitted from my deceased father's will including a statement that I was never his son (I was his illegitimate son).
Can the threat of divorce from his wife at the time his will was drawn (in effect disowning me) be grounds for action against estate?

I doubt that would be UNDUE influence, BUT yoiu may have another ground -- mistake of fact -- to contest the Will.