  NGC 300 ULX1 is a newly identified ultra-luminous X-ray pulsar. The system is
associated with the supernova impostor SN 2010da that was later classified as a
possible supergiant Be X-ray binary. In this work we report on the spin period
evolution of the neutron star based on all the currently available X-ray
observations of the system. We argue that the X-ray luminosity of the system
has remained almost constant since 2010, at a level above ten times the
Eddington limit. Moreover, we find evidence that the spin period of the neutron
star evolved from ~126 s down to ~18 s within a period of about 4 years. We
explain this unprecedented spin evolution in terms of the standard accretion
torque theory. An intriguing consequence for NGC 300 ULX1 is that a neutron
star spin reversal should have occurred a few years after the SN 2010da event.
