I'm Peter Dell and I'm awfully irritable (11)

I believe the answer is:

illtempered

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

'irritable' is the definition.
(I've seen this before)

'i'm peter dell and i'm awfully' is the wordplay.
'i'm peter dell' anagrams to 'ILLTEMPERED'.
But, I'm not clear how this is indicated.

Can you help me to learn more?

(Another definition for illtempered that I've seen is " Irritable".)

I've seen this clue in The Irish Independent.

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