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We present new optical data on the cluster AX J2019+1127 identified by theX-ray satellite ASCA at z\sim 1 (Hattori et al. 1997). The data suggest thepresence of a high-redshift cluster of galaxies responsible for the largeseparation triple quasar MG2016+112. Our deep photometry reveals an excess ofz\sim 1 galaxy candidates, as already suspected by Benitez et al. (1999). Ourspectroscopic survey of 44 objects in the field shows an excess of 6 redgalaxies securely identified at z \sim 1, with a mean redshift of z =1.005 +/-0.002. We estimate a velocity dispersion of \sigma = 771 (+430/-160) km s(-1)based on these 6 galaxies and a V-band mass-to-light ratio of 215 (+308/-77)h_50 M/L_sol. Our observations thus confirm the existence of a massivestructure acting as the lens, which explains the unusual configuration of thetriple quasar. Hence, there is no more need to invoke the existence of a ``darkcluster'' to understand this lens system.Comment: 8 pages, 4 figures, uses aa.cls, accepted to Astronomy and  Astrophysics with minor change

Spectroscopic confirmation of a cluster of galaxies at $\vec{z=1}$ in the field of the gravitational lens MG 2016+112