First author of the paper, Karsten Brogaard of SAC, explains: "The only way we can explain what we have observed in this system is by assuming that two stars are orbiting each other so closely that one some 40 million years back in time stole some mass from the other, turning the victim into a naked and somewhat inflated white dwarf."
The two stars are orbiting with a period of only 1.44 day, and there are indications that in another 100 million years another transfer of mass will occur; this time the other way around, with the white dwarf beginning to steal mass form what at that time will be it's red giant companion.
At the end of this the two stars will embrace each other in a cosmic hug and turn into a single super heavy star.
"If someone at that time observes the final result, it will mimic a young and heavy star on the outside, but inside it will feel very ancient," Karsten finishes.
The full paper is here: https://arxiv.org/abs/1809.00705
The image shows NGC6791, with the star V106 marked in red.