Observing the Principal putting on headgear, just because... (6,4)

I believe the answer is:

seeing that

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

'because' is the definition.
(thesaurus)

'observing the principal putting on headgear' is the wordplay.
I cannot really understand how this works, but
'observing' could be 'seeing' (I've seen this before) and 'seeing' is located in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is located in the answer.
'on' could be 'at' (I've seen this in other clues) and 'at' is present in the answer.
A single letter 'h' remains which might be clued in a way I don't see.
This explanation may well be incorrect...

'just' acts as a link.

Can you help me to learn more?

I've seen this clue in The Irish 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.