A new absorption spectrum has been found in the flash photolysis of H$_3$BCO which, from its structure and the observed isotope shifts can be unambiguously assigned to the free BH$_2$ radical. The spectrum represents a transition similar to those previously observed in NH$_2$ and CH$_2$. The molecule is linear in the excited state but bent (with an angle of 131$^\circ$) in the ground state. Molecular constants and geometrical data are evaluated. The electronic transition is $^2$B$_1$($\Pi_u$)-$^2$A$_1$ and fits well with expectation from the Walsh diagram for XH$_2$ molecules.