Por --- que sea

por amigo que sea
por fuerte que sea
por joven/viejo que sea

Context would help.
But maybe:

por amigo que sea: however good a friend he/she is
por fuerte que sea: however strong it/he/she is
por joven/viejo que sea: however young/old it/he/she is

Here is the context:

'No estoy muy seguro de haber guardado la compostura debida a un Excelentísimo y Magnífico Rector en despacho oficial después de semejante revelación, por amigo que sea'

I'm still wishing for more context but maybe something like:

After such a revelation, I'm not certain I kept the composure expected of an "Excelentísimo y Magnífico Rector" acting officially, even though I am a good friend.

Or:

...I'm not certain he/she kept the composure expected...even though he/she is a good friend.