Multiple sources connected to the MTV show tell us "The Hills: New Beginnings" is officially not coming back for a third season, and late last week the cast got the bad news from production.

There are a few reasons the reboot met its demise: one source close to the show tells us producers recently explored the thought of bringing younger cast members into the fold to diversify things, but several of the original stars were not on board.

We're told some of those OGs also had major issues with the reboot ... believing it wasn't the show MTV promised them, and feeling like it was, at times, forced with fake storylines and confessionals. Our sources say some of the OGs refused to continue to play along, which ultimately led to the cancelation.

All in all ... we're told many of them said the reboot didn't have the same feel as their first go-round and it created an impasse between some stars and the network.

However, another source blames the cancelation on COVID-19 ... citing all the hurdles in booking filming locations for a big ensemble cast while following social distancing protocols. We're told producers feel like they squeezed as much juice from the lemon as possible, given the dynamics.

"The Hills: New Beginnings" was rebooted in 2019 with Audrina Patridge, Brody Jenner, Heidi Montag, Spencer and Stephanie Pratt, Whitney Port, Brandon Thomas Less, Kaitlynn Carter, Frankie Delgado, Justin Brescia, Jason and Ashley Wahler and former 'O.C.' star Mischa Barton.

But the biggest star was always missing ... Lauren Conrad ... who, as we first told you, was too busy with her other business ventures to join the reboot.

The OG show aired from 2006 to 2010 ... and while the reboot wasn't as impactful, we're told producers were proud of what they were able to do in the middle of the worldwide pandemic.