Bindi Irwin is celebrating Father's Day and showing love for 3 men who are pillars in her life, but there's someone else who is causing her great pain ... her own grandfather. Bindi posted a heartfelt tribute Sunday ... "Appreciation post for the three most incredible fathers in my life. My dad, my husband and my father-in-law. My dad taught me the importance of strength when standing up for what I believe in and to have empathy for all living beings. My husband amazes me every day with his kind and steadfast heart, his love for our daughter is infinite. My father-in-law works tirelessly for his family and is always there with a word of encouragement. These extraordinary men inspire me and I love them so very much."