They are both pantherine or roaring cats. There are 5 species, and they are the lion, tiger, leopard, jaguar and snow leopard. They evolved from a common ancestor closely related to the clouded leopard, a medium sized cat. All cats big and small share a common ancestor, but the roaring cats share an ancestor more recently than any of them does with, say, the cheetah, house cat, ocelot, bobcat and cougar.
If 2 different species last shared an ancestor recently, they may not have evolved to be so different that they can no longer interbreed with each other. Nevertheless, in nature, 2 different species, even if they can produce hybrids, usually refuse to interbreed. The reason for their refusal is that each species is adapted to a different lifestyle and environment, and their hybrids would not be as well adapted to the lifestyle or environment of either parent. As a result they do not compete well with either species, and because of that individuals that do not make sure they mate only with their own species will end up leaving fewer descendants. Over many generations, those that do not observe species boundaries will be weeded out.
To help them avoid being weeded out and to make sure each species only mates with individuals of the same species, most species have evolved ways to recognize individuals of the same species. Moths and snakes for example evolve different phermones, so that only individuals of the same species will be attracted to the phermones of their own species. Humans too release phermones to attact each other. Although we cannot smell our own phermones, we are nevertheless attracted by it and it changes our behavior subconsciously. Other kinds of animals such as birds may use plumage colors and/or songs to identify each other. Frogs use different mating calls to find their own species. Scientists call these ways different species use to avoid interbreeding "pre-mating isolation" mechanisms.