  The chromomagnetic interaction, with proper account for flavour-symmetry
breaking, is shown to explain the mass and coupling properties of the X(3872)
resonance as a $J^{PC}$ = 1$^{++}$ state consisting of a heavy quark-antiquark
pair and a light one. It is crucial to introduce all the spin-colour
configurations compatible with these quantum numbers and diagonalise the
chromomagnetic interaction in this basis. This approach thus differs from the
molecular picture $D\bar {D}*$ and from the diquark-antidiquark picture.
