Ashton Kutcher and Mila Kunis have released a video explaining why they asked a judge for leniency when sentencing their former co-star for raping two women.
The Hollywood actors also said they didn't mean to "undermine the testimony of the victims" and apologised if they had "retraumatised them in any way".
Danny Masterson, who starred alongside Kunis and Kutcher in That 70s Show, has been ordered to serve 30 years to life behind bars.
One victim described him as "pathetic, disturbed and completely violent".
Letters later emerged that reveal ex-cast members, as well as siblings, wrote letters in support of Masterson - with Kunis describing him as a " role model" and Kutcher saying he was "dedicated and loyal".
In an Instagram video posted on Saturday night, Kutcher and Kunis took it to turns to explain why the letters were sent.
Kutcher said: "We are aware of the pain that has been caused by the character letters that we wrote on behalf of Danny Masterson."
Kunis added: "We support victims, we have done this historically through our work and will continue to do so in the future."
Kutcher went on to say that Masterson's family had reached out to them asked them to write "character letters to represent the person that we knew for 25 years".
He added that this was so the judge could "take that into full consideration relative to sentencing".
Kunis then said: "The letters were not written to question the legitimacy of the judicial system or the validity of the jury's ruling."
Kutcher continued: "They were intended for the judge to read and not to undermine the testimony of the victims or retraumatise them in any way, we would never want to do that and we're sorry if that has taken place."
Kunis finished the video by saying: "Our heart goes out to every single person who has ever been a victim of sexual assault, sexual abuse or rape."
In his letter, Kutcher had described the convicted rapist as a "dedicated and loyal" husband and father and addressed the career-ending accusations against the 47-year-old.
"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," he wrote.
"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."
Kutcher - who is married to Kunis - went on to claim that Masterson "was the first person to jump to the defence" of a girl he didn't know after she was berated by her belligerent boyfriend.
In her letter, Kunis wrote: "Throughout our time together, Danny has proven to be an amazing friend, confidant, and, above all, an outstanding older brother figure to me."
She went on to claim that Masterson had played a "pivotal role" in guiding her away from drug use.
Masterson played Steven Hyde, Kunis played Jackie Burkhart, and Kutcher played Michael Kelso in the sitcom that ran between 1998 and 2006.
Masterson's wife, Bijou Phillips, said in her letter to the judge that he had been a "life-saving partner".
She wrote: "Our daughter and I are heartbroken that he is not home with us. It has been very difficult without him here. Even though he is now in jail, he calls her every day."
The one-time actor's legal team is vowing to appeal - and if unsuccessful, Masterson would not be eligible for parole until he is a pensioner.
During the trial, the women whose evidence led to his conviction said Masterson had given them drinks that made them feel light-headed in 2003, before they passed out and he raped them.