Keira Knightley has accused the Duchess of Cambridge of masking the "bloody, screaming" reality of childbirth following her polished appearances hours after delivery.
The actress, 33, reportedly gave birth to daughter Edie a day before Kate had her second child, Princess Charlotte, in 2015.
In an essay entitled The Weaker Sex, published in feminist collection Feminists Don't Wear Pink (And Other Lies), Knightley recounted in graphic detail her own birth experience and how it appeared to differ from the royal's.
"She was out of hospital seven hours later with her face made up and high heels on," Knightley wrote. "The face the world wants to see. Hide.
"Hide our pain, our bodies splitting, our breasts leaking, our hormones raging. Look beautiful, look stylish, don't show your battleground, Kate."
The royal's flawless appearance shortly after the birth of her three children has stirred debate online, with some praising the duchess of her quick turnover and others saying she was setting unrealistic expectations for women.
Knightley wrote: "Seven hours after your fight with life and death, seven hours after your body breaks open, and bloody, screaming life comes out. Don't show. Don't tell."
The Bend It Like Beckham star also described her own birth experience in vivid detail.
"My vagina split. You came out with your eyes open. Arms up in the air. Screaming," she wrote. "They put you on to me, covered in blood, vernix, your head misshapen from the birth canal. Pulsating, gasping, screaming.
"You latched on to my breast immediately, hungrily, I remember the pain. The mouth clenched tight around my nipple, light sucking on and sucking out.
"I remember the s***, the vomit, the blood, the stitches. I remember my battleground. Your battleground and life pulsating. Surviving. And I am the weaker sex? You are?"
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Knightley's swipe at the Duchess of Cambridge comes after she revealed she had a mental breakdown and was diagnosed with post-traumatic stress disorder as she struggled with the pressures of fame at a young age.
The actress, who soared to A-list status with roles in the Pirates Of The Caribbean series and Pride & Prejudice, said she went through therapy to cope with her growing celebrity.