This Lion & his family had already killed the preceding night & he had a full belly. The poor Wildebeeste stumbled into the snoozing lion pride after crossing a small river & though satiated the lions couldn't help themselves & had to have a go. The image was taken just as this subadult male released its throttle grip of the suffocated Wildebeeste's muzzle.
Certainly not serendipity for the Wildebeeste!!