how should this sentence be.

" Richard III supposedly had the young princes murdered. Never found out what really happened to them."

The second group of words lacks a subject.

Here's one way to correct it.

Richard III supposedly had the young princes murdered, but no one ever found out what really happened to them.

HE SUBMITTING HIS RESIGNATION TO HIS SUPERVISOOR AT THE SAME TIME.

iS THIS A SENTENCE FRAGMENT?

To go a long way without water

The provided sentence appears to be two separate statements, so here are a few options to combine them into one coherent sentence:

1. "Richard III supposedly had the young princes murdered, but their fate remains unknown."
2. "According to historical accounts, Richard III allegedly orchestrated the murder of the young princes, leaving their true fate a mystery."
3. "The fate of the young princes, supposedly murdered by Richard III, has never been definitively determined."

Remember, when combining sentences, it's important to maintain clarity and coherence to ensure the intended meaning is conveyed effectively.