We present spatially resolved measurements of the stellar initial mass function ( IMF ) in NGC 1399 , the largest elliptical galaxy in the Fornax Cluster . Using data from the Multi Unit Spectroscopic Explorer ( MUSE ) and updated state-of-the-art stellar population synthesis models from [ ] , we use full spectral fitting to measure the low-mass IMF , as well as a number of individual elemental abundances , as a function of radius in this object . We find that the IMF in NGC 1399 is heavier than the Milky Way in its centre and remains radially constant at a super-salpeter slope out to 0.7 R _ { \mathrm { e } } . At radii larger than this , the IMF slope decreases to become marginally consistent with a Milky Way IMF just beyond R _ { \mathrm { e } } . The inferred central V-band M/L ratio is in excellent agreement with the previously reported dynamical M/L measurement from [ ] . The measured radial form of the M/L ratio may be evidence for a two-phase formation in this object , with the central regions forming differently to the outskirts . We also report measurements of a spatially resolved filament of ionised gas extending 4 \arcsec ( 404 pc at D _ { \mathrm { L } } = 21.1 Mpc ) from the centre of NGC 1399 , with very narrow equivalent width and low velocity dispersion ( 65 \pm 14 kms ^ { -1 } ) . The location of the emission , combined with an analysis of the emission line ratios , leads us to conclude that NGC 1399 ’ s AGN is the source of ionising radiation .