How does marriage / divorce affect a previously written Will?
Generally speaking under Singapore law, if you get married, your previous Will are automatically revoked upon marriage. This is because you have a new family and the law assumes that you wish to provide for your new family.
Take for example you have loving siblings whom you want leave something behind for. You write a Will as based on your circumstances the Singapore's default Intestate succession laws do not cover them. The moment you get married (including remarriage) *POOF* they get NOTHING!
Divorce however, does NOT revoke the Will.
Going by another example, you used to love your "then" spouse and have written a Will giving him/her 100% of all your assets. He/she cheats on you and thankfully after a nasty divorce you still manage to keep some of your matrimonial assets. Life is cruel. If you did not update your Will and die, it's about to be a whole lot more cruel when your ex-spouse becomes a proud beneficiary of 100% of your assets.
This is one of the many reasons why it is especially important to update your Will when your life's circumstances change.