Panthera leo, was the European Cave Lion, which grew over one third to even twice the size of an African Lion, larger than any of the Lions we know living today. This means they were essentially a giant amongst Lion species. They would have been silent ambush predators, and cave art shows that they were indeed white, like the snow. Such a camouflage adaptation would of course aid in stalking prey over snowscapes, much the same as Polar Bears do today (Polar Bears go back to the Ice Age to) The European Cave Lion had a North American cousin called the American Cave Lion that lived and died when the European died out.
Cave Lions lived from around 950,000 Years Ago - 9,000 Years Ago. Along with almost all major 'Ice Age Giants', they became extinct at the end of the Last Ice Age Glacial period, as the Ice Caps retreated and the climate warmed up. Perhaps the remaining populations of Panthera leo became isolated, and their cave bound lifestyle (like the Neanderthals - Homo neanderthalensis) made them susceptible to extinction, due to their now unnecessary white fur coats and the difficult distribution of breeding individuals. Some say, as for all Ice Age Mega-fauna, that humans played there part in wiping out the Panthera leo. What we cannot say is that this would have been entirely likely, but what we can say is that humans did arrive as these animals began to decline, and they must have hunted some of the animal species to some extent.
The Mammoths start walking in the Ice Age and a baby Mammoth is with its mother and a Panthera leo spots the baby Mammoth, but has to be careful not to get too close to the adult. Later a lone traveling male Woolly Mammoth finds a pair of Panthera Leos feasting on a victim, it wasn't a Mammoth calf, but a human. The Panthera leo get out of the male Mammoth's way.