  We present LAMOST~J041920.07+072545.4 (hereafter J0419), a close binary
consisting of a bloated extremely low mass pre-white dwarf (pre-ELM WD) and a
compact object with an orbital period of 0.607189~days. The large-amplitude
ellipsoidal variations and the evident Balmer and He~I emission lines suggest a
filled Roche lobe and ongoing mass transfer. No outburst events were detected
in the 15 years of monitoring of J0419, indicating a very low mass transfer
rate. The temperature of the pre-ELM, $T_\mathrm{eff} = 5793_{-133}^{+124}\,\rm
K$, is cooler than the known ELMs, but hotter than most CV donors. Combining
the mean density within the Roche lobe and the radius constrained from our SED
fitting, we obtain the mass of the pre-ELM, $M_1 = 0.176\pm 0.014\,M_\odot$.
The joint fitting of light and radial velocity curves yields an inclination
angle of $i = 66.5_{-1.7}^{+1.4}$ degrees, corresponding to the compact object
mass of $M_2 = 1.09\pm 0.05\,M_\odot$. The very bloated pre-ELM has a smaller
surface gravity ($\log g = 3.9\pm 0.01$, $R_1 = 0.78 \pm 0.02\,R_\odot$) than
the known ELMs or pre-ELMs. The temperature and the luminosity ($L_\mathrm{bol}
= 0.62_{-0.10}^{+0.11}\,L_\odot$) of J0419 are close to the main sequence,
which makes the selection of such systems through the HR diagram inefficient.
Based on the evolutionary model, the relatively long period and small $\log g$
indicate that J0419 could be close to the "bifurcation period" in the orbit
evolution, which makes J0419 to be a unique source to connect ELM/pre-ELM WD
systems, wide binaries and cataclysmic variables.
