New mum Kate opened up about the "intense" and "difficult" day on social media, as celebrities flocked to celebrate with their mothers.
She wrote on her Instagram stories: "Another very intense day on socials for anyone without a Mum, without a child, for those who cannot have children, those who don't have good relationships with their mum.
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Kate is step-mum to Rio's three children from his marriage to late wife RebeccaCredit: Refer to Caption
"The step mums who aren't recognised, people who have had recent losses in their families and couldn't possibly celebrate.
"I am thinking of you all, it's a tough day in the calendar for many."