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We present observations of ASASSN-19dj, a nearby tidal disruption event (TDE)discovered in the post-starburst galaxy KUG 0810+227 by the All-Sky AutomatedSurvey for Supernovae (ASAS-SN) at a distance of d $\simeq98$ Mpc. We observedASASSN-19dj from $-$21 to 392 d relative to peak ultraviolet (UV)/opticalemission using high-cadence, multiwavelength spectroscopy and photometry. Fromthe ASAS-SN $g$-band data, we determine that the TDE began to brighten on 2019February 6.8 and for the first 16 d the rise was consistent with a flux$\propto t^2$ power-law. ASASSN-19dj peaked in the UV/optical on 2019 March 6.5(MJD = 58548.5) at a bolometric luminosity of $L = (6.2 \pm 0.2) \times 10^{44}\text{ erg s}^{-1}$. Initially remaining roughly constant in X-rays and slowlyfading in the UV/optical, the X-ray flux increased by over an order ofmagnitude $\sim$225 d after peak, resulting from the expansion of the X-rayemitting region. The late-time X-ray emission is well fitted by a blackbodywith an effective radius of $\sim1 \times 10^{12} \text{ cm}$ and a temperatureof $\sim6 \times 10^{5} \text{ K}$. The X-ray hardness ratio becomes softerafter brightening and then returns to a harder state as the X-rays fade.Analysis of Catalina Real-Time Transient Survey images reveals a nuclearoutburst roughly 14.5 yr earlier with a smooth decline and a luminosity of$L_V\geq1.4 \times 10^{43}$ erg s$^{-1}$, although the nature of the flare isunknown. ASASSN-19dj occurred in the most extreme post-starburst galaxy yet tohost a TDE, with Lick H$\delta_{A}$ = $7.67\pm0.17$ \AA.

Discovery and Follow-up of ASASSN-19dj: An X-ray and UV Luminous TDE in an Extreme Post-Starburst Galaxy