Adjoint linear operators and inner products question; why does $\langle T(x),T(x)\rangle =\langle T^*T(x),x\rangle $?

Question

I have seen this multiple times in my textbook; $\langle T(x),T(x)\rangle=\langle T^*T(x),x\rangle$; why is this true?

I know the definition of adjoint is if $\langle x,T(y)\rangle=\langle T^*(x),y\rangle$. But I don't see the connection.

Thanks