The Transiting Exoplanet Survey Satellite (tess) produces a large number of single-transit event candidates, since the mission monitors most stars for only $sim$27,days. Such candidates correspond to long-period planets or eclipsing binaries. Using the tess Sector 1 full-frame images, we identified a 7750,ppm single-transit event with a duration of 7,hours around the moderately evolved F-dwarf star tic (Tmag=10.23, teff=6280$pm{85}$,K). Using archival WASP photometry we constrained the true orbital period to one of three possible values. We detected a subsequent transit-event with NGTS, which revealed the orbital period to be 38.20,d. Radial velocity measurements from the CORALIE Spectrograph show the secondary object has a mass of $M_2$= $0.148pm{0.003}$,M$_{odot}$, indicating this system is an F-M eclipsing binary. The radius of the M-dwarf companion is $R_2$ = $0.171pm{0.003}$,R$_{odot}$, making this one of the most well characterised stars in this mass regime. We find that its radius is 2.3-$sigma$ lower than expected from stellar evolution models.
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