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We report the detection of the likely companion of the binary millisecondpulsar J0740+6620 with the Gran Telescopio Canarias in the $r'$ and $i'$ bands.The position of the detected starlike source coincides with the pulsarcoordinates within the 1$\sigma$ uncertainty of $\approx$ 0.2 arcsec. Itsmagnitudes are $r'=26.51\pm0.17$ and $i'=25.49\pm0.15$. Comparing the data withthe white dwarf cooling tracks suggests that it can be an ultracoolhelium-atmosphere white dwarf with the temperature $\lesssim$ 3500 K andcooling age $\gtrsim$ 5 Gyr. The age is consistent with the pulsarcharacteristic age corrected for kinematic effects. This is the reddest sourceamong known white dwarf companions of millisecond pulsars. Detection of thesource in other bands would be useful to clarify its properties and nature.

The ultracool helium-atmosphere white dwarf companion of PSR J0740+6620?