Both sides
Bhagavad-gita As It Is
BG Chapters 1 - 6
BG 2.14, Purport:
The two different names of address given to Arjuna are also significant. To address him as Kaunteya signifies his great blood relations from his mother's side; and to address him as Bhārata signifies his greatness from his father's side. From both sides he is supposed to have a great heritage. A great heritage brings responsibility in the matter of proper discharge of duties; therefore, he cannot avoid fighting.