We report the discovery of J1953 - 1019 , the first resolved triple white dwarf system .
The triplet consists of an inner white dwarf binary and a wider companion .
Using Gaia DR2 photometry and astrometry combined with our follow-up spectroscopy , we derive effective temperatures , surface gravities , masses and cooling ages of the three components .
All three white dwarfs have pure-hydrogen ( DA ) atmospheres , masses of 0.60 - 0.63 \mbox { $ \mathrm { M } _ { \odot } $ } and cooling ages of 40 - 290 Myr .
We adopt eight initial-to-final mass relations to estimate the main sequence progenitor masses ( which we find to be similar for the three components , 1.6-2.6 \mathrm { M } _ { \odot } ) and lifetimes .
The differences between the derived cooling times and main sequence lifetimes agree for most of the adopted initial-to-final mass relations , hence the three white dwarfs in J1953 - 1019 are consistent with coeval evolution .
Furthermore , we calculate the projected orbital separations of the inner white dwarf binary ( 303.25 \pm 0.01 au ) and of the centre of mass of the inner binary and the outer companion ( 6 398.97 \pm 0.09 au ) .
From these values , and taking into account a wide range of possible configurations for the triplet to be currently dynamically stable , we analyse the future evolution of the system .
We find that a collision between the two inner white dwarfs due to Lidov-Kozai oscillations is unlikely , though if it occurs it could result in a sub-Chandrasekhar Type Ia supernova explosion .