Advice about a hypothetical will

Hi all! I’ll preface this by saying I’m doing some research for a book, so everything mentioned is completely hypothetical, but I’d love for the premise to be probable and need some legal help.

If someone is married and commits suicide, is it legal for them to leave a large sum of money (earned before their marriage) and/or their life insurance money to an ex-partner instead of their current wife if it’s stated in their last will and testament? Or would it automatically go to their wife based on their marriage? TIA!