Avril Lavigne and Mod Sun Split, Call Off Engagement

Avril Lavigne and Mod Sun are no longer together, she's made the tough decision to call off their engagement almost a year after he proposed ... TMZ has learned.

Sources close to the now-former couple tell us the two had tried to make things work recently, going "on and off" over the last few months, but it just wasn't right. We're told not only have they hit the brakes on getting married -- they're no longer together as a couple, either.

At this time, it's unclear what led to the split ... but we're told there was no cheating on either side.

The news comes on the heels of photos of Avril out to dinner with Tyga and a group of friends Sunday night at NOBU.

We're told Tyga and Avril appeared extremely comfortable hanging out, and shared a hug in the parking lot before leaving in the same vehicle. The sources we've spoken to say the two are good friends, and have been for some time, but it's nothing romantic.

An interesting note, however, is Mod's rep tells us, "They were together and engaged as of 3 days ago when he left for tour so if anything has changed that's news to him."

Avril and Mod got engaged last year in March during a trip to Paris. He recently released a new album titled "God Save the Teen" with a handful of songs dedicated to Avril.

Avril and Mod were recently spotted together at an event for The Grammys ... just a couple weeks before he left to go on tour.