Japanese phrase
二人だけの話だよ。 futa ri da ke no hanashi da yo
Meaning
This is just between the two of us.
When to use it
Marks information as private between two people. It sounds casual and asks for discretion, so it fits friends or family more than formal situations.
Example dialogue
妹の誕生日プレゼント、もう用意した？ imōto no tan jō nichi pu re ze n to mō yō i shi ta
Have you got your sister's birthday present ready?
うん、でも二人だけの話だよ。 u n de mo futa ri da ke no hanashi da yo
Yes, but this is just between the two of us.