Ashton Kutcher has resigned from Thorn, an organization he founded in 2009 with then-wife Demi Moore that works to combat child sexual abuse. The move comes nearly a week after he and his wife, Mila Kunis, acknowledged the "pain" they caused by writing character reference letters in support of convicted rapist Danny Masterson, with whom they co-starred in Fox sitcom "That '70s Show."

"Ashton Kutcher, our co-founder, will be resigning from his role as Board Chair at Thorn, effective immediately," the nonprofit organization said in a statement Friday. "This 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."

Thorn also included Kutcher's resignation letter, dated Thursday.

"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," his letter begins. "I cannot allow my error in judgment to distract from our efforts and the children we serve.

"As you know, I have worked for 15 years to fight for people who are sexually exploited," his letter 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."

The letter concluded with: "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. 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."

Time was the first to report the news, and said Kunis, who served as an observer on the board, also stepped down.

Mila Kunis, Ashton Kutcher asked Danny Masterson's judge for leniency in his sentencing

After Masterson — who played Hyde on "That '70s Show" — was sentenced to 30 years to life in prison Sept. 8 for the rapes of two women two decades ago, The Hollywood Reporter revealed Kunis and Kutcher were among several of Masterson's former costars who wrote character reference letters urging the judge in his case to offer the actor leniency.

In his letter dated July 27, Kutcher described Masterson as a man who treated people "with decency, equality, and generosity." Kunis' letter called Masterson "an outstanding role model and friend" and an "exceptional older brother figure."

"While I'm aware that the judgment has been cast as guilty on two counts of rape by force and the victims have a great desire for justice, I hope that my testament to his character is taken into consideration in sentencing," Kutcher's letter reads. "I do not believe he is an ongoing harm to society, and having his daughter raised without a present father would (be) a tertiary injustice in and of itself."

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The couple said they didn't intend to 'undermine the testimony' of Masterson's victims

In a video posted Sept. 9 on Kutcher's Instagram account, he and Kunis addressed the letters, and said Masterson's family had approached the couple after the actor's conviction in May and asked them to represent "the person that we knew for 25 years," 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. "We support victims. We have done this historically through work and will continue to do so in the future."

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

Added Kunis: "Our heart goes out to every single person who has ever been a victim of sexual assault, sexual abuse or rape."

Contributing: Kim Willis

Danny Mastersonsentenced to 30 years to life in prison for 2 rapes