Bright and nearby ( 22 pc ) solar-type dwarf \kappa For ( HIP 11072 ) is a triple system .
The close pair of M-type dwarfs Ba , Bb with a tentative period of 3.7 days moves around the main component A on a 26-year orbit .
The mass of the “ dark companion ” Ba+Bb is comparable to the mass of A , causing large motion of the photo-center .
The combined spectro-interferometric orbit of AB is derived and the relative photometry of the components A and B is given .
A weak signature of Ba and Bb is detected in the high-resolution spectra by cross-correlation and by variable emission in the Bahlmer hydrogen lines .
The activity of the M-dwarfs , manifested by a previously detected radio-flare , is likely maintained by synchronisation with their tight orbit .
We discuss the frequency of similar hidden triple systems , methods of their detection , and the implications for multiple-star statistics .