  Stellar pulsation theory provides a means of determining the masses of
pulsating classical Cepheid supergiant - it is the pulsation that causes their
luminosity to vary. Such pulsational masses are found to be smaller than the
masses derived from stellar evolution theory: this is the Cepheid mass
discrepancy problem, for which a solution is missing. An independent, accurate
dynamical mass determination for a classical Cepheid variable star (as opposed
to type-II Cepheids, low-mass stars with a very different evolutionary history)
in a binary system is needed in order to determine which is correct. The
accuracy of previous efforts to establish a dynamical Cepheid mass from
Galactic single-lined noneclipsing binaries was typically about 15-30 per cent,
which is not good enough to resolve the mass discrepancy problem. In spite of
many observational efforts, no firm detection of a classical Cepheid in an
eclipsing double-lined binary has hitherto been reported. Here we report the
discovery of a classical Cepheid in a well detached, double-lined eclipsing
binary in the Large Magellanic Cloud. We determine the mass to a precision of
one per cent and show that it agrees with its pulsation mass, providing strong
evidence that pulsation theory correctly and precisely predicts the masses of
classical Cepheids
