I was told that it had been sick for some time, and until recently was thought to be in the hospital (I've not heard anything since about three weeks ago, but interestingly it wasn't listed in the inventory last December.) A few weeks ago they brought in a pair African brush-tailed porcupines instead.
Sorry, I just meant that they'd brought them into the Gorilla Kingdom enclosure - I think this is the pair previously displayed in Zoo World though I had never seen them properly, and I hadn't seen any signage indicating that they were on display for some time.