Ellie was your mother. Dina was your other mother because of them being married. During a huge mission to avenge her father, Joel, she left you. When they finally came back, you only saw dina and no ellie. Dina gave you a letter from Ellie. It read: My daughter, i'm sorry that i couldn't tell you goodbye, one last time. If Dina is giving you this, i lost my battle during seattle. My daughter, my beautiful, beautiful girl. I'm sorry it had to bring you the news this way. I love you baby girl.