Ashton Kutcher has stepped down from an anti-child sex abuse nonprofit that he co-founded. The move comes following backlash over the letters that he and his wife Mila Kunis wrote to the judge presiding over Danny Masterson's sexual assault trial ahead of his sentencing last week. 

The 45-year-old actor resigned his position as chairman of the board of Thorn, an organization that he founded in 2009 with then-wife Demi Moore. According to Time, Kunis, 42, also stepped down from her role as an observer on the board. On Friday, Thorn posted Kutcher's letter of resignation on its website.

"After my wife and I spent several days of listening, personal reflection, learning, and conversations with survivors and the employees and leadership at Thorn, I have determined the responsible thing for me to do is resign as Chairman of the Board, effectively immediately," Kutcher wrote in the letter, which was dated Thursday. "I cannot allow my error in judgment to distract from our efforts and the children we serve."

ashton kutcher on red carpet

Ashton Kutcher resigned from an anti-child sexual abuse organization that he co-founded following the controversy over the letter he wrote in support of his former co-star Danny Masterson. (Kevin Winter/Getty Images)

He continued, "Victims of sexual abuse have been historically silenced and the character statement I submitted is yet another painful instance of questioning victims who are brave enough to share their experiences. This is precisely what we have all worked to reverse over the last decade."

ASHTON KUTCHER AND MILA KUNIS APOLOGIZE FOR ‘PAIN’ CAUSED BY THEIR LETTERS IN SUPPORT OF DANNY MASTERSON

"The mission must always be the priority and I want to offer my heartfelt apology to all victims of sexual violence and everyone at Thorn who I hurt by what I did," he added. "And to the broader advocacy community, I am deeply sorry. I remain proud of what we have accomplished in the past decade and will continue to support Thorn’s work. 

"Thank you for your tireless advocacy and dedication to this cause," Kutcher concluded.

ashton kutcher speaking during senate foreign relations hearing

Kutcher, who co-founded the Thorn nonprofit with his then-wife Demi Moore in 2009, served as chairman of the board until his resignation on Thursday. He is pictured speaking on behalf of the organization during a Senate Foreign Relations Committee hearing in 2017. (Paul Morigi/WireImage)

In its post, the organization noted that "the decision is rooted in the recognition of recent events and ensuring Thorn remains focused on its mission: to build technology to defend children from sexual abuse."

Kutcher and Kunis starred alongside Masterson, 47, in the hit sitcom "That 70s Show" from 1998 to 2006.  

In addition to Kunis and Kutcher, almost 50 other individuals wrote letters on behalf of Masterson to the judge presiding over his sexual assault trial ahead of his sentencing on September 7.  Masterson's wife, Bijou Phillps, and fellow "That 70s Show" co-stars Debra Jo Rupp and Kurtwood Smith were among those who sent character letters to Los Angeles Superior Court Judge Charlaine F. Olmedo.

In an excerpt from Kutcher's letter, which was obtained by Fox News Digital, he described Masterson as a "role model."

Ashton Kutcher in black tuxedo and Mila Kunis in a black dress on the carpet

Kutcher's wife Mila Kunis, who also wrote a character letter for Masterson, also stepped down from her position as an observer on the board, according to Time. (Axelle/Bauer-Griffin/FilmMagic/Getty Images)

"Danny takes his job seriously. He is kind, courteous, and hard working(sic)," Kutcher wrote. "He treated everyone from the grips to the teamsters to the actors to the caterers as equals. As a role model, Danny has consistently been an excellent one."

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In an excerpt from her letter, Kunis noted that Masterson had become an "outstanding older brother figure" to her during their friendship.

Kunis wrote that she would "wholeheartedly vouch for Danny Masterson's exceptional character and the tremendous positive influence he has had on me and the people around him."

Ashton Kutcher smiles in a sweater and tie next to Mila Kunis in a red shirt next to Danny Masterson in 2000

Kutcher and Kunis starred alongside Masterson, 47, in the hit sitcom "That 70s Show" from 1998 to 2006.   (Chris Weeks/Liaison/Getty Images)

Masterson was sentenced to 30 years to life after being convicted on two counts of forcible rape. He is being held at the Los Angeles County Sheriff's Men's Central Jail as he awaits his transfer to a California state prison.

Following Masterson's sentencing, Kutcher and Kunis issued public apologies for the "pain" caused by the letters in a joint video that was shared on the "No Strings Attached" star's instagram page.

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"We are aware of the pain that has been caused by the character letters that we wrote on behalf of Danny Masterson," Kutcher said while seated next to his wife.

"We support victims. We have done this historically through our work and will continue to do so in the future," Kunis added.

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"A couple of months ago, Danny's family reached out to us and they asked us to write character letters to represent the person that we knew for 25 years so that the judge could take that into full consideration relative to the sentencing," Kutcher said.

"The letters were not written to question the legitimacy of the judicial system, or the validity of the jury’s ruling," Kunis said.

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"They were intended for the judge to read and not to undermine the testimony of the victims or re-traumatize them in any way," Kutcher added. "We would never want to do that, and we’re sorry if that has taken place."

"Our heart goes out to every single person who’s ever been a victim of sexual assault, sexual abuse or rape," Kunis said at the conclusion of the video.

Representatives for Kutcher, Kunis and Moore did not immediately respond to Fox News Digital's request for comment.