How does Ralph know about the Castle's secret garden entrance?

Background

After beating Mermaid's Cave, you're sent to Ambi's Palace to invade while Queen Ambi is gone.

Once at the castle gates, Ralph is already there.

Ralph mentions a secret entrance:

There should be a hidden entrance in the palace garden! I'll sneak in through there!

After, Ralph explicitly says:

What? "Why do I know about the hidden passage on my first trip here?" Nevermind!!! I'm coming, Nayru!!!

How did Ralph know about this secret passage? It doesn't seem to be explained in-game. Is there any background to this?

zelda-oracle-of-ages

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