Allison Mack, the former "Smallville" actress and high-ranking member of the cultlike group Nxivm who was sentenced to three years in prison in 2021, was released Monday, the Federal Bureau of Prisons said in online records.

Mack was arrested in 2018 along with several other Nxivm leaders, including Keith Raniere, who was convicted of racketeering charges.

Raniere, the founder of Nxivm, was sentenced to 120 years in prison in 2020. Mack pleaded guilty to racketeering and racketeering conspiracy charges one month before Raniere's 2019 trial was set to begin.

US District Judge Nicholas Garaufis previously called Mack "an essential accomplice" and a "willing and proactive ally" of Raniere, but also said, "I don't doubt that you were manipulated and also felt captive."

Nxivm, a company based in Albany, New York, touted "self-help" classes.

But prosecutors said within the organization a secretive, female-only group was created that ultimately led to some women being branded with Raniere and Mack's initials and being coerced into giving compromising information, including nude photos, to the group's leaders on a regular basis.

The group, known as DOS, involved several women referred to as "first-line masters," who reported directly to Raniere and recruited other women as their slaves, according to trial testimony.

Unbeknownst to many of the women, Raniere was the head of the group, and women were, at times, directed to have sex with him and send him nude photographs.

In the letter of apology filed ahead of her sentencing, Mack wrote that she does not take lightly the responsibility she has for the lives she negatively impacted.

"I lied to you, again and again, in order to protect the delusion I was so deeply committed to believing," she wrote.