  DDO68 (UGC5340) is an unusual dwarf galaxy with extremely low gas metallicity
(12+log(O/H) = 7.14) residing in the nearby Lynx-Cancer void. Despite its
apparent isolation, it shows both optical and HI morphological evidence for
strong tidal disturbance. Here, we study the resolved stellar populations of
DDO68 using deep images from the HST archive. We determined a distance of
12.75+-0.41 Mpc using the tip of the red giant branch (TRGB). The star
formation history reconstruction reveals that about 60 per cent of stars formed
during the initial period of star formation, about 12-14 Gyr ago. During the
next 10 Gyr DDO68 was in the quenched state, with only slight traces of star
formation. The onset of the most recent burst of star formation occurred about
300 Myr ago. We find that young populations with ages of several million to a
few hundred million years are widely spread across various parts of DDO68,
indicating an intense star formation episode with a high mean rate of 0.15
Msun/yr. A major fraction of the visible stars in the whole system (~80 per
cent) have low metallicities: Z = Zsun/50 - Zsun/20. The properties of the
northern periphery of DDO68 can be explained by an ongoing burst of star
formation induced by the minor merger of a small, gas-rich, extremely
metal-poor galaxy with a more typical dwarf galaxy. The current TRGB-based
distance of DDO68 implies a total negative peculiar velocity of ~500 km/s.
