  The dispersal of the circumstellar discs of dust and gas surrounding young
low- mass stars has important implications for the formation of planetary
systems. Photo- evaporation from energetic radiation from the central object is
thought to drive the dispersal in the majority of discs, by creating a gap
which disconnects the outer from the inner regions of the disc and then
disperses the outer disc from the inside-out, while the inner disc keeps
draining viscously onto the star. In this Letter we show that the disc around
TW Hya, the closest protoplanetary disc to Earth, may be the first object where
a photoevaporative gap has been imaged around the time at which it is being
created. Indeed the detected gap in the ALMA images is consistent with the
expectations of X-ray photoevaporation models, thus not requiring the presence
of a planet. The photoevaporation model is also consistent with a broad range
of properties of the TW Hya system, e.g. accretion rate and the location of the
gap at the onset of dispersal. We show that the central, unresolved 870 {\mu}m
continuum source might be produced by free free emission from the gas and/or
residual dust inside the gap.
