Family fortune divided by the Spanish on the quiet (13)

I believe the answer is:

clandestinely

I'm a little stuck... Click here to teach me more about this clue!

'on the quiet' is the definition.
(both can mean in secret)

I cannot understand how the rest of the clue works.

(Other definitions for clandestinely that I've seen before include "Secretly" , "Covertly" , "In a secret manner" , "Sly cent in deal (anag) - on the sly" .)

I've seen this clue in The Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.