The Duchess reportedly stressed how important good manners and respect are, before referring to the impact of social media, saying trolls have a girl versus girl mentality.
She apparently claimed "vicious and hurtful" online trolling is responsible for pitting women against each other, and went on to say people need to stand against it.
Fergie, whose daughters Princess Beatrice and Princess Eugenie have for years been subject to social media bullying, reportedly pleaded with readers to "be kinder".
She then urged people to seriously consider what they post online, before encouraging people to call out any unacceptable behaviour.
Fergie concluded her earnest message by asking readers to remember the saying: "if you can’t say anything nice, don’t say anything at all."