There's been talk about black panthers and pumas being in Australian bush for years. From what I've seen, there have been many witness sightings in and around the Grampians area of Victoria, Otway Ranges, and WA. Theories abound but the main 3 are:

On point 3, around 15 years ago there were several lynx' found in suburban Melbourne (out in Mt. Waverley). They grew too big to handle and would hunt possums. Nobody knows what happened to them in the end, but as stated above, it isn't impossible to imagine that of the several dozen or so illegal exotic animals that are trafficked into Australia, that most--if not all--would eventually be driven out to the bush and released once they become too difficult to handle (obviously this is cruel and we'd prefer they be handed in to a zoo for proper care, but people are also keen to avoid a jail sentence).

While point 2 above sounds like folklore, it is well-documented that in the Northern Territory, an African pygmy hippo was found and shot dead. It had been surviving in the Australian bush for 6 years, after the millionaire zoo-owner shut its doors (how or why it escaped is beyond me. Source: https://www.news.com.au/national/pygmy-hippopotamus-shot-during-northern-territory-hunting-trip/news-story/1461ccca27470bd37db65d0d46ac51f2 )

Now, after all these years and many sightings (including some photo proof going around where clearly a puma or big cat of some description is in the photo or video), a doco is coming out to explore more of this situation that once upon a time was largely passed off as folklore, but increasingly there seems to be more to these stories than anybody could have imagined. For reference, here's info about the doco: https://www.newcastleherald.com.au/story/6741620/hunting-for-clues-of-mystery-black-panthers/

I'm pumped to watch this!