it was (third-person singular neuter past of być)

(idiomatic) it's water under the bridge; it's water over the dam

(idiomatic) for what it's worth, for the record, for clarity's sake, just so you know, I'll have you know, just so it's clear

(idiomatic) quod erat demonstrandum

(colloquial, idiomatic) add insult to injury, for the worse, as if that weren't enough

third-person singular neuter conditional of być