Upright supporter of the Knights Templar (4)

I believe the answer is:

stem

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

'upright supporter' is the definition.
'stem' can be an answer for 'supporter' (I've seen this before). I'm not certain of the 'upright' bit.

'of the knights templar' is the wordplay.
'of' says the answer is hidden in the clue.
'STEM' is hidden within 'knights templar'.

Can you help me to learn more?

(Other definitions for stem that I've seen before include "race" , "Peduncle" , "Stalk - check" , "Main part of noun or verb" , "Dam" .)

I've seen this clue in the Evening Standard.

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