I have been mourning the loss of my twin brother for over 20 years and I realized that having and losing a twin is a life and bereavement like no other. This relationship of gemellity that has developed from our conception is not as simple as you would think, hence, the thought of writing about this particular link unifying the twins from beginning to demise. To do so, I recruited about sixty twins, including individuals who have lost their twin brother or sister in utero or at birth for some, and throughout their lives for others. I also asked for the collaboration of Mr Fabrice Bak, PhD in Psychology, well-known gemellologist and founder and director of Cabinet Bak & Associés, located in Lyon, in France. Mr Bak is, among others, a specialist of twin development and a member of the scientific committee of the Fédération Jumeaux et Plus, in France Whether you are a twin, a parent, a partner, a friend of a duo or a trio, the reading of this book will allow you to find out about the hidden face of gemellity, uncovered through literature and touching testimonies of twins, in mourning or not, including triplets.