Have you ever seen something like this ?

We have a cactus growing in Langebaan which for the first time ever is flowering. As you can see on the photo the flower is already taller than the double storey house and I'm not sure if it has finished growing yet. We rescued the cactus from the rubbish dump about 8 years ago and this is the first time it has ever flowered. I noticed 2 smaller ones in another garden in Langebaan also flowering so I'm not sure what conditions have now occurred that have caused them to now flower. I don't even know it's name to be able to google it.