King Shantanu had three sons: Bhishma (Devavrata), Chitrangada, and Vichitravirya. Dhritarashtra was born much later to Queen Ambika (Vichitravirya's widow) through Sage Vyasa under the Niyoga practice, making him Shantanu's grandson, not his son. Chitrangada and Vichitravirya were both biological sons of Shantanu, while Bhishma was his son through Ganga.