She wore a pale yellow coat-dress by Alexander McQueen as she arrived at the St George’s Chapel earlier this morning.
It was the first public appearance since welcoming her third baby, Prince Louis, back in April.
However, Kate’s wardrobe choice raised eyebrows as it appeared to look white in some shots.
“You never wear white at a wedding unless you are a bride”
Viewers called out the Duchess for attempting to upstage Meghan on her big day.
One person tweeted: “I swear if Kate was at my wedding and she turned up in white she would get punted out quicker than you could f***ing say Royal Wedding.”
Another added: “I can’t believe Kate has gone and worn white/cream on the day of another Royal Wedding.”
A third commented: “WHY IS KATE WEARING WHITE!?!?! You never wear white at a wedding unless you are a bride.”
While a fourth person wrote: “Kate Middleton wearing white? Kinda shady. #RoyalWedding.”
And a fifth joined in: “Why is Kate wearing white? Send her home, #royalwedding.”