'SLOMW' Demi Engemann Back as 'Friend Of' But Filmed Heavily for Season 4

Demi Engemann may only be a "friend of" the cast in season 4 of "The Secret Lives of Mormon Wives" ... but TMZ has learned she filmed far more than a typical part-time player.

Sources close to production tell us the exiled cast member's role goes well beyond the usual drop-in appearances. We're told Demi was mic'd up for multiple events and logged significant camera time before her involvement eventually tapered off.

Demi starred in the first two seasons before being iced out of the "MomTok" circle after her friendship with costar Jessi Draper imploded. The rift followed a "Vanderpump Villa" crossover, where rumors swirled that both women were involved with 'VV' star Marciano Brunette while in relationships. Demi denied an affair, while Jessi admitted to hers -- fueling much of season 3's drama.

She later made a few intense cameos in Season 3, sparking speculation she'd return in a bigger way ... possibly leaning into a villain arc. Our sources say she’ll be popping up again this season ... just not in a full-time capacity.

As we first reported ... Marciano filed a lawsuit claiming Demi spread defamatory information about their alleged relationship. Demi has asked a judge to dismiss the case, arguing it was filed "solely to gain media attention."

Season 4 premieres March 12, and with Demi back in the mix, even in a limited role, the MomTok drama looks far from over.