Learn Spanish (Latin America): El príncipe supo de la traición ayer. - The prince found out about the treason yesterday.

This happens because saber is a mental verb that changes its meaning depending on the past tense you use. When you use it in the preterite tense (supo), it focuses on the exact moment the action was completed. The exact moment you "know" something for the first time is when you "find out" or "discover" it.

How would this sentence change if the prince already had the knowledge beforehand?

If he already knew about it, you would use the imperfect tense: El príncipe sabía de la traición. The imperfect (sabía) describes an ongoing state of mind in the past, which translates as "knew." However, because this sentence includes ayer (yesterday), it points to a specific event that happened that day, making the preterite supo (found out) a much better fit.

Why use de here instead of sobre to say "about"?

While sobre does mean "about," using de is the standard, most natural way to say you found out, heard, or knew "about" something in Spanish. Just like hablar de means "to talk about," the phrase saber de means "to know about" or "to find out about."

Is supo an irregular verb?