Somehow, he always knew this moment would come. Despite the defeat of Voldemort thirteen years ago, Dumbledore always said he would return; and Dumbledore's judgement was one he trusted. Of course he would be back. It was just a matter of time.
Nevertheless, Remus Lupin started significantly when a large black dog bounded into his London flat with this very news.
On June 24th, 1995, the Dark Lord returned.