We report on the detection of hydromagnesium isocyanide, HMgNC, in the laboratory and in the carbon rich evolved star IRC+10216. The J=1-0 and J=2-1 lines were observed in our microwave laboratory equipment in Valladolid with a spectral accuracy of 3
,KHz. The hyperfine structure produced by the Nitrogen atom was resolved for both transitions. The derived rotational constants from the laboratory data are $B_0$=5481.4333(6),MHz, $D_0$=2.90(8),KHz, and $eQq(N)$=-2.200(2),MHz. The predicted frequencies for the rotational transitions of HMgNC in the millimeter domain have an accuracy of 0.2-0.7,MHz. Four rotational lines of this species, J=8-7, J=10-9, J=12-11 and J=13-12, have been detected towards IRC+10216. The differences between observed and calculated frequencies are $<$0.5,MHz. The rotational constants derived from space frequencies are $B_0$=5481.49(3),MHz and $D_0$=3.2(1),KHz, i.e., identical to the laboratory ones. A merged fit to the laboratory and space frequencies provides $B_0$=5481.4336(4),MHz and $D_0$=2.94(5),KHz. We have derived a column density for HMgNC of (6$pm$2)$times10^{11}$,cm$^{-2}$. From the observed line profiles the molecule have to be produced produced in the layer where other metal-isocyanides have been already found in this source. The abundance ratio between MgNC and its hydrogenated variety, HMgNC, is $simeq$20.
