  We present the discovery of a pair of transiting giant planets, TOI-216b and
c, using four sectors of TESS photometry. TOI-216 is a $0.87 M_{\odot}$ dwarf
orbited by two transiters with radii of $8.2 R_{\oplus}$ and $11.3 R_{\oplus}$,
and periods of $17.01$d and $34.57$d, respectively. Anti-correlated TTVs are
clearly evident indicating that the transiters orbit the same star and interact
via a near 2:1 mean motion resonance. By fitting the TTVs with a dynamical
model, we infer masses of $26_{-11}^{+24} M_{\oplus}$ and $190_{-80}^{+220}
M_{\oplus}$, establishing that the objects are planetary in nature and have
likely sub-Kronian and Kronian densities. TOI-216 lies close to the southern
ecliptic pole and thus will be observed by TESS throughout the first year,
providing an opportunity for continuous dynamical monitoring and considerable
refinement of the dynamical masses presented here. TOI-216 closely resembles
Kepler-9 in architecture, and we hypothesize that in such systems these
Saturn-analogs failed to fully open a gap and thus migrated far deeper into the
system before becoming trapped into resonance, which would imply that future
detections of new analogs may also have sub-Jupiter masses.
