  Context: We present the transit and follow-up of a single transit event from
Campaign 14 of K2, EPIC248847494b, which has a duration of 54 hours and a 0.18%
depth. Aims: Using photometric tools and conducting radial velocity follow-up,
we vet and characterise this very strong candidate. Methods: Owing to the long,
unknown period, standard follow-up methods needed to be adapted. The transit
was fitted using Namaste, and the radial velocity slope was measured and
compared to a grid of planet-like orbits with varying masses and periods. These
used stellar parameters measured from spectra and the distance as measured by
Gaia. Results: Orbiting around a sub-giant star with a radius of
2.70$\pm$0.12R$_{\rm Sol}$, the planet has a radius of
1.11$_{-0.07}^{+0.07}$R$_{\rm Jup}$ and a period of 3650$_{-1130}^{+1280}$
days. The radial velocity measurements constrain the mass to be lower than
13M$_{\rm Jup}$, which implies a planet-like object. Conclusions: We have found
a planet at 4.5 AU from a single-transit event. After a full radial velocity
follow-up campaign, if confirmed, it will be the longest-period transiting
planet discovered.
