  Because many classical Be stars may owe their nature to mass and
angular-momentum transfer in a close binary, the present masses, temperatures,
and radii of their components are of high interest for comparison to stellar
evolution models. Kappa Dra is a 61.5-day single-lined binary with a B6 IIIe
primary. With the CHARA Array instruments MIRC/MIRC-X and MYSTIC, we detected
the secondary at (approximately photospheric) flux ratios of 1.49 +- 0.10% and
1.63 +- 0.09% in the H and K band, respectively. From a large and diverse
optical spectroscopic database only the radial velocity curve of the Be star
could be extracted. However, employing the parallaxes from Hipparcos and Gaia,
which agree within their nominal 1-sigma errors, we could derive the total mass
and found component masses of 3.65 +- 0.48 Msun and 0.426 +- 0.043 Msun for the
Be star and the companion, respectively. Previous cross-correlation of the
observed far-UV spectrum with sdO spectral model templates had not detected a
companion belonging to the hot O-type subdwarf (sdO) population known from ~20
earlier-type Be stars. Guided by our full 3D orbital solution, we found a
strong cross-correlation signal for a stripped subdwarf B-type companion
(far-UV flux ratio of 2.3 +- 0.5%), enabling the first firm characterization of
such a star, and making kappa Dra the first mid- to late-type Be star with a
directly-observed subdwarf companion.
