"Revenge" star Christa B. Allen is rebuilding her life after one particularly troublesome relationship ... saying she's escaped the clutches of an alleged "cult leader."

The actress-turned-TikTok star posted the eyebrow-raising life update to her account Wednesday, opening up about the past romance -- but didn't name names.

She did, however, hint at her ex's identity ... noting the manipulator was "charismatic" and "wealthy" ... and she's now repairing her life after he "burned it to the ground."

In the caption, Christa confessed she partially blames herself for getting caught up with this shady figure ... and is asking herself the hard questions in the aftermath.

She wrote ... "why did I trust him? why did I hand over my power? why did I silence my own inner knowing? the truth is, he was selling fairytales and from luxurious penthouses and private jets, I foolishly bought in."

Christa wrote she spent every waking moment with this person, who she said "lies as easily as they breathe"  ... but didn't realize the scale of the deception at the time.

Though, Christa said she eventually learned the truth, a revelation that both "shattered" her and forced her to rebuild her life.

Christa -- who fans may recognize as Jennifer Garner's younger self in "13 Going on 30" -- admitted she wasn't ready to share the full story ... but hinted she may one day.

We've reached out to Christa's rep for comment ... so far, no word back.