Jon Gosselin Engaged to Longtime Girlfriend Stephanie Lebo

Jon Gosselin is walking down the aisle once again ... 'cause he's officially engaged to his girlfriend of three years Stephanie Lebo.

The reality television star and his bride-to-be announced the news to Entertainment Tonight Thursday ... revealing Gosselin got down on one knee last Saturday at her fav restaurant in Pennsylvania.

Jon popped the question in front of both of their parents, professing his love for Stephanie and sliding the ring on her finger.

Everyone at the table reportedly got very emotional ... with Stephanie's dad apparently bawling his eyes out at the sight of his little girl getting engaged.

BTW ... this won't come as a shock to fans of Gosselin -- who told People in April he planned to propose within a year.

Of course, Jon was famously married to Kate Gosselin from 1999 to 2008 ... with their marriage the subject of the hit reality show "Jon & Kate Plus 8."

Their relationship has been a bit rocky in recent years ... with the two parents splitting custody of their sextuplets and two other kids.

We recently talked to Jon about his ex-wife's relationship with their son Collin back in September ... and, he went in on Kate -- watch the video to hear all his thoughts.