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We present TYC 2505-672-1 as a newly discovered and remarkable eclipsingsystem comprising an M-type red giant that undergoes a ~3.45 year long,near-total eclipse (depth of ~4.5 mag) with a very long period of ~69.1 yr. TYC2505-672-1 is now the longest-period eclipsing binary system yet discovered,more than twice as long as that of the currently longest-period system,$\epsilon$ Aurigae. We show from analysis of the light curve including both ourown data and historical data spanning more than 120 yr and from modeling of thespectral energy distribution, both before and during eclipse, that the redgiant primary is orbited by a moderately hot source (T$_{eff}$~8000 K) that isitself surrounded by an extended, opaque circumstellar disk. From the measuredratio of luminosities, the radius of the hot companion must be in the range0.1-0.5 Rsun (depending on the assumed radius of the red giant primary), whichis an order of magnitude smaller than that for a main sequence A star and 1-2orders of magnitude larger than that for a white dwarf. The companion istherefore most likely a "stripped red giant" subdwarf-B type star destined tobecome a He white dwarf. It is however somewhat cooler than most sdB stars,implying a very low mass for this "pre-He-WD" star. The opaque disk surroundingthis hot source may be a remnant of the stripping of its former hydrogenenvelope. However, it is puzzling how this object became stripped, given thatit is at present so distant (orbital semi-major axis of ~24 AU) from thecurrent red giant primary star. Extrapolating from our calculated ephemeris,the next eclipse should begin in early UT 2080 April and end in mid UT 2083September (eclipse center UT 2081 December 24). This system is poised to becomean exemplar of a very rare class of systems, even more extreme in severalrespects than the well studied archetype $\epsilon$ Aurigae.

An Extreme Analogue of $\epsilon$ Aurigae: An M-giant Eclipsed Every 69 Years by a Large Opaque Disk Surrounding a Small Hot Source