Last will how do we know which is last will

Hi, My dad has two sons, me and my brother. He had made a will in 2010 giving all his property to me and my brother 50:50 equally. He has for last 5 years been staying with my brother. I live abroad and help my brother with money. My dad's mental health has deteriorated substantially. How do I check that my brother has not hot my dad to make and register another will leaving everything in my brothers name. How do I confirm which is my dad's last will? Thanks