The singer dropped "Why Why Why" late on Thursday, addressing for the first time how he almost became a parent with one of his exes. As Shawn put it in the song ... he was told about the possible pregnancy and it seriously freaked him out ... as he was "still a kid" at the time.

Shawn, who is now 26, never names the ex in question ... but does note the romance came during a particularly tough time when he struggled with his mental health.

He sings ... "I stepped off the stage with nothin' left, All the lights were f***in' with my head."

The singer has had several notable relationships since catapulting to fame in 2014. His most significant relationship was with Camila Cabello, who he dated on and off for the past 5 years.

In fact, the former flames had a brief reunion this summer, when they were spotted together at the Copa América final in Miami in July -- though the duo didn't share any PDA while at the soccer match ... and haven't been spotted together since.

During the off-periods of their love story, Shawn was notably linked to Sabrina Carpenter and Charlie Travers. He also spent a bunch of quality time with Hailey Bieber in 2018 ... before she apparently gave him the boot to marry Justin Bieber that same year.