たら最後(さいご)Once, Now that, As soon as

たら最後(さいご) and たが最後(さいご) are grammar structures that both share the meaning of 'once (A), definitely (B)'. (B) will always be something negative that is thought to inevitably occur once the action of (A) happens. These expressions may be translated as 'once (A), (B)', 'now that (A), (B)', or 'as soon as (A), (B)'.

Both たら and が are being used as conjunction particles. たら carries its usual meaning of 'if' or 'when', while が has the meaning of 'however', or 'but'. This means that たが最後(さいご) means '(A), but it will end up as (B)', while たら最後(さいご) means 'when (A), it will end up as (B)'. Although this nuance is slightly different, they are used completely interchangeably.

Because 最後(さいご) is primarily seen before the comma in these types of sentences, it can be easy to think that it is connected to the が or たら. However, it is actually more correctly connected logically to the (B) half of the sentence, and states that the 'final state' will end up being that way.

Caution

Occasionally, the (B) phrase will be omitted from these sentences when the negative result is obvious.