Justin Bieber did not reach out to Selena Gomez to comfort her as she underwent kidney transplant surgery ... because he had no idea it was happening.

Separate Justin and Selena sources tell us Selena did not share the news with Justin because they have had no connection or contact in a long time.

As you know, they're members of the same church -- Hillsong -- but they never interact with each other. We're told the church has actually facilitated keeping them separate.

As one source flatly put it, "They don't talk. Period." It's unclear if Justin and Selena feel this way, but people around them are annoyed the public thinks there's still a connection between the 2. One source says, "It was a childhood thing. They've both had other relationships. It's over."