This paper proposes a qualitative and quantitative solution of a long-standing problem in astrophysics: the origin of the knee in the Galactic cosmic ray (GCR) spectrum. We calculate GCR flux averaged over Supernova explosion energies and types, applying only the formulae of the standard model of CR acceleration in Supernova remnants (SNR) and the latest astronomical data on the variety in Supernovae. For this purpose we estimate the distribution of SNe in explosion energies and show this distribution to be probably a very asymmetric function with large dispersion. In the case under consideration the cosmic ray flux in the whole energy range should be predominantly formed by the most energetic SN explosions. The knee in the GCR spectrum at energy around $E_{\rm knee}=3$ PeV can quantitatively be explained by the dominant contribution of Hypernovae. The model sketches the all-particle cosmic ray spectrum up to 1018 eV.