  Long-period comet C/2018 F4 (PANSTARRS) was observed to show duplicity of its
inner region in 2020 September, suggestive of a splitting event. We here
present analyses of our observations of the comet taken from the LOOK project
and the University of Hawaii 2.2 m telescope after the discovery of the
splitting. The two fragments Components A and B, estimated to be $\sim\!60$ m
to 4 km in radius, remained highly similar to each other in terms of
brightness, colour, and dust morphology throughout our observing campaign from
2020 September to 2021 December. Our fragmentation model yielded that the two
components split at a relative speed of $3.00 \pm 0.18$ m s$^{-1}$ in 2020 late
April, implying a specific energy change of $\left(5.3 \pm 2.8 \right) \times
10^3$ J kg$^{-1}$, and that Component B was subjected to a stronger
nongravitational acceleration than Component A in both the radial and normal
directions of the orbit. The obtained splitting time is broadly consistent with
the result from the dust morphology analysis, which further suggested that the
dominant dust grains were millimeter-sized and ejected at speed $\sim\!2$ m
s$^{-1}$. We postulate that the pre-split nucleus of the comet consisted of two
lobes resembling the one of 67P, or that the comet used to be a binary system
like main-belt comet 288P. Regardless, we highlight the possibility of using
observations of split comets as a feasible manner to study the bilobate shape
or binarity fraction of cometary nuclei.
