  In this paper, we investigate the integrability aspects of a physically
important nonlinear oscillator which lacks sufficient number of Lie point
symmetries but can be integrated by quadrature. We explore the hidden symmetry,
construct a second integral and derive the general solution of this oscillator
by employing the recently introduced $\lambda$-symmetry approach and thereby
establish the complete integrability of this nonlinear oscillator equation from
a group theoretical perspective.
