Fanning, who also starred with Stewart in Joan Jett biopic The Runaways, spoke out in support of her friend who was snapped kissing the director in July (12) behind the back of her long-term boyfriend Robert Pattinson.
The teen actress criticised the public backlash from the scandal and defended her co-star's right to privacy.
She tells InStyle magazine, ""Everyone thinks they have the right to, you know, publicise the struggles and sadness and heartbreak and all of that... It's like, 'Why do you think you are the authority to judge people's experiences?'.""
Stewart issued a public apology after the pictures were published and insisted she was ""deeply sorry"" for her ""momentary indiscretion"".