'Sister Wives' Star Kody Brown and Wife Robyn Are Not Returning to the Show

Tough news for longtime fans of "Sister Wives" star Kody Brown and his one remaining wife, Robyn ... the couple is NOT returning for the upcoming season of the popular TLC reality show.

TLC just dropped the season 21 trailer, and right off the bat they told fans Kody and Robyn would no longer be involved.

It's a huge shocker ... Kody and Robyn have been 'Sister Wives' staples ... appearing on the show for the past 16 years.

The two have yet to comment on their dramatic exit.

As you know, the series has for years been tracking Kody -- a polygamist -- and his wives, along with their large combined family, including Kody's exes Christine, Janelle, and Meri and their numerous kids.

Christine, Janelle, and Meri all had a spiritual awakening of sorts and, over time, they cut ties with Kody ... leaving Robyn as his lone remaining wife.

In the season 21 trailer, Christine, Jennelle and Meri seem somewhat stunned as they muse about Kody and Robyn's exit ... but the trailer also shows the three moving on with other men as they dive into new relationships.

Interesting plot twist for the new season ... now all we need is to hear from Kody and Robyn.