If you and your ex had not divorced, and he pre-deceased you intestate ...in other words, "without a will"...all the family assets would go to you, the surviving spouse. Your children would not get anything until you die. Unless you have a will that specifies otherwise, any remaining assets upon your death would be equally distributed to your children.

What your ex has done is basically the same thing.

If his second wife pre-deceases him, who is the executor? Typically it is the oldest child.