It's a long story (4)

I think it could be either:

yarn

saga

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

'long story' is the definition.
(a saga is a long and complicated story)

'it's a' is the wordplay.
'it's' becomes 'sag' (I can't explain this - if you can you should believe this answer much more).
'sag'+'a'='SAGA'

Can you help me to learn more?

(Other definitions for saga that I've seen before include "Epic tale" , "Chronicle; adventure" , "Norse epic" , "Lengthy tale" , "Epic - legend" .)

I've seen this clue in the Evening Standard, The New York Times, The Washington Post, the USA Today, the Newsday, the Universal, The Wall Street Journal and The Guardian.

Want a hint initially instead of a full solution? Install my app