We present a comparison of the nitrogen-to-oxygen ratio (N/O) in 37 high-redshift galaxies at $z\sim$2 taken from the KMOS Lensed Emission Lines and VElocity Review (KLEVER) Survey with a comparison sample of local galaxies, taken from the Sloan Digital Sky Survey (SDSS). The KLEVER sample shows only a mild enrichment in N/O of $+$0.1 dex when compared to local galaxies at a given gas-phase metallicity (O/H), but shows a depletion in N/O of $-$0.36dexwhencomparedatafixedstellarmass(M$*$).Wefindastronganti-correlationinlocalgalaxiesbetweenN/OandSFRintheM$*$-N/Oplane,similartotheanti-correlationbetweenO/HandSFRfoundinthemass-metallicityrelation(MZR).Weusethisanti-correlationtoconstructafundamentalnitrogenrelation(FNR),analogoustothefundamentalmetallicityrelation(FMR).WefindthatKLEVERgalaxiesareconsistentwithboththeFMRandtheFNR.ThissuggeststhatthedepletionofN/Oinhigh-$z$ galaxies when considered at a fixed M$\ast$ is driven by the redshift-evolution of the mass-metallicity relation in combination with a near redshift-invariant N/O-O/H relation. Furthermore, the existence of an fundamental nitrogen relation suggests that the mechanisms governing the fundamental metallicity relation must be probed by not only O/H, but also N/O, suggesting pure-pristine gas inflows are not the primary driver of the FMR, and other properties such as variations in galaxy age and star formation efficiency must be important.