Fra' Andrew Bertie, "Fra'?"

I regret I must report the death of “Fra’ Andrew Bertie,” more fully “His Most Eminent Highness Fra’ Andrew Bertie,” Prince of the Church, head of the Knights of Malta. A fine man by all accounts.

What does “Fra’” mean?

Brother.

‘fra: A title of address for a friar or monk, a shortened form of frate, brother.’

From here .
And upon preview: Dayamn! Too slow.

Thank you. Latin I presume? Italian?

I think the practice originated among Italian monks (e.g. Fra Angelico), but it works either way: frater in Latin, frate or fratello in Italian. Nowadays it’s commonly used in fraternal organizations.