  Despite the universe containing primordial thorium (Th) of sufficient
abundance to appear in stellar spectra, detection of Th has to date been
tentative and based on just a few weak and blended lines. Here, we present
convincing evidence not only for the first Th detection in a magnetic
chemically peculiar Ap star but also for the first detection of Th III in a
stellar spectrum. CPD-62 2717 was initially recognized as a highly-magnetized
Ap star thanks to resolved magnetically split lines captured in $H$-band
spectra from the SDSS/APOGEE survey. The star was subsequently pinpointed as
extraordinarily peculiar when careful inspection of the $H$-band line content
revealed the presence of five lines of Th III, none of which are detected in
the other $\sim1500$ APOGEE-observed Ap stars. Follow-up with the VLT+UVES
confirmed a similarly peculiar optical spectrum featuring dozens of Th III
lines, among other peculiarities. Unlike past claims of Th detection, and owing
to high-resolution observations of the strong ($\sim$8$-$12$\,$kG) magnetic
field of CPD-62 2717, the detection of Th III can in this case be supported by
matches between the observed and theoretical magnetic splitting patterns.
Comparison of CPD-62 2717 to stars for which Th overabundances have been
previously reported (e.g., Przybylski's Star) indicate that only for CPD-62
2717 is the Th detection certain. Along with the focus on Th III, we use time
series measurements of the magnetic field modulus to constrain the rotation
period of CPD-62 2717 to $\sim$4.8 years, thus establishing it as a new example
of a super-slowly-rotating Ap star.
