FundMECFSTIL: The largest known species of cats is the Liger, hybrid of a male Lion and female Tiger
Not a species. The males are infertile so they cannot breed new ligers.
Which is why the title says extant feline, not species.
That’s not the actual definition of species (for example, assume a formerly viable species was reduced to three infertile members), but ask them biologists to define species and you’ll get twelve answers so whatever