If you had asked him when he was younger what death was, Regulus certainly would have never said that it was a deserted island.
Well, not so deserted now that he was on it.
Less deserted when Dumbledore washed up one day.
Regulus looked up to see the aged Headmaster dragging himself out from the surf, shoes squishing unpleasantly, trying to rub sand and seawater out of his ears. Regulus had to admit, he would never have expected Dumbledore of all people to show up.
"What are you doing here?" Regulus asked the man, watching as he started ringing out his periwinkle blue robes.
Dumbledore looked at him levelly, taking in his presence, registering it, briefly pondering it. Then he turned his attention back to drying off. "Severus killed me."
Regulus blinked. "Severus? But I thought--"
"It's a long story," Dumbledore interrupted pleasantly. "One that can wait until after I stop dripping."
Regulus nodded, treating the old man's word as law as always. Even when they'd technically been enemies, it was hard for him not to obey Dumbledore if he instructed something. This had made battles very confusing for him and had no doubt contributed at least in part to his death.
After several more moments, Regulus spoke again. "Excuse me sir. But... Why are you here? I thought the whole point of this island was that I'm supposed to be alone. Banished from... wherever it is most people go. Or something."
Dumbledore wondered over this and said, "Well, I could just be a hallucination."
"Can dead people hallucinate?"
"Well, I can't be certain. After all, I've never been dead before."
Regulus nodded, seeing that it was ridiculous to question Dumbledore about something that he didn't know very much about. After all, Regulus should know more about death. He'd had more experience with it.
Now stuck in awkward silence, Regulus does the only thing that he thinks makes sense after the greatest wizard of his age has washed up on his island and told him that he was dead.