on his, her, or their side; in support of him, or them
Yo estuve de su lado aún en contra de mi padre.
I was on his side even against my father.
¿Por qué siempre tiene que estar de su lado?
Why does he always have to be on their side?
— Voces Inocentes (2005)
Y la verdad está de su lado, amigo.
And the truth is on your side, my friend.
Los Poderes Supremos no estarán de su lado en esto.
The Powers That Be will not be on his side in this.
— Guardianes Del Día (2006)
Tal vez el destino estaba ahora de su lado.
Perhaps fate was on their side now.
— भाग मिल्खा भाग (2013)
I'm on your side.