Mumbai, August 3 (IANS) Hollywood star Sandra Bullock marked Sister's Day with a touching tribute to her sister, Gigi, and said that she is the woman who knows her best. Sandra shared a string of pictures with her sister and called her a "brilliant soul". Sandra said she feels fortunate to have someone who knows her "missteps and all" yet continues to love her every single day, while also celebrating both biological and chosen sisters. Happy Sisters Day. International Sisters Day is celebrated annually on the first Sunday of August, honoring the unique bond shared by biological sisters, cousins, and close friends who feel like family.