Like Titanic in reality (2,6)

I believe the answer is:

at bottom

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'in reality' is the definition.
Both the definition and answer are adverbs. Maybe there's an association between them I don't understand?

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for at bottom that I've seen before include "Location of 27 28" , "Like the Titanic" , "Basically" .)

I've seen this clue in The Independent.

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