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It arises a puzzle in \NGC\, how to secularly maintain the counter-rotatingdisc from $0.2$ to $7\,$pc unambiguously detected by recent ALMA observationsof molecular gas. Upon further analysis of disc dynamics, we find that theKelvin-Helmholtz (KH) instability (KHI) results in an unavoidable catastropheof the disc developed at the interface between the reversely rotating parts,and demonstrate that a close binary of supermassive black holes provides tidaltorques as the unique external sources to prevent the disc from the KHcatastrophe. We are led to the inescapable conclusion that there must be abinary black hole at the center of NGC 1068, to prevent it from the KHcatastrophe. The binary is composed of black holes with a separation of$0.1\,$pc from GRAVITY/VLTI observations, a total mass of $1.3\times10^{7}\:M_{\odot}$ and a mass ratio of $\sim 0.3$ estimated from the angularmomentum budge of the global system. The KHI gives rise to forming a gapwithout cold gas at the velocity interface which overlaps with the observed gapof hot and cold dust regions. Releases of kinematic energies from the KHI ofthe disc are in agreement with observed emissions in radio and $\gamma$-rays.Such a binary is shrinking with a timescale much longer than the local Hubbletime via gravitational waves, however, the KHI leads to an efficientannihilation of the orbital angular momentum and speed up merge of the binary,providing a new paradigm of solving the long term issue of "final parsecproblem". Future observations of GRAVITY+/VLTI are expected to be able tospatially resolve the CB-SMBHs suggested in this paper.

Dynamical evidence of the sub-parsec counter-rotating disc for a close binary of supermassive black holes in the nucleus of NGC 1068