Carpenter, who played Cordelia on the hit show and spin-off "Angel", accused Whedon of creating a "toxic and cruel" atmosphere on set and abusing his power.
She also called him "mean and biting" and "toxic and cruel," accusing him of "pitting people against one another to compete and vie for his attention and approval."
Following her shocking claims, Michelle Trachtenberg also made allegations against Whedon - claiming that he wasn't allowed to be alone with her on set.
Boreanaz - who starred with Carpenter on "Buffy" and "Angel" - took to Twitter over the weekend (13-14Feb21) to offer his support to the actress, writing, "I am here for you to listen and support you. Proud of your strength."
And Carpenter replied, "I know you're there for me, David. I appreciate all you've done to demonstrate that support privately as well. Especially since Wednesday... thank you so much."
Their allegations came several months after "Justice League" star Ray Fisher accused Whedon of being unprofessional on the set of the DC blockbuster he took over when director Zack Snyder was forced to step down due to a family tragedy.
In response to Carpenter's shocking allegations, the Cyborg depicter wrote on Twitter, "I am forever grateful for her courage and for her lending her voice to the Justice League investigation. Read her truth. Share her truth. Protect her at all costs."