Keep William informed (4)

I believe the answer is:

tell

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

'keep william' is the definition.
'tell' can be an answer for 'william' (I've seen this before). I am not certain of the 'keep' bit.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for tell that I've seen before include "Count - recount" , "Issue instructions" , "Grass - Swiss hero" , "work in a bank" , "Relate (a story)" .)

I've seen this clue in the Evening Standard.

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