27-year-old Kate, who is stepmother to 40-year-old Rio's three children, Lorenz, 12, and Tate, ten, included an image of herself and the children's grandparents.
Captioning the sweet image, which was shared to Instagram, she wrote: 'Lovely Mother’s Day dinner with family, we celebrated all 6 of us today.
'How lucky we all are to have hearts that can love after so much pain. Happy Mother’s Day to everyone.'
Kate would have wanted to include Rebecca in the children's thoughts as she helped to navigate them through what is no doubt an incredibly painful day for them.
Earlier in the day, Rio, has gushed over his fiancé Kate, for keeping the memory of his children's mother alive on Mother's Day.
The footballer shared a snap of Kate walking along a deck while holding hands with his daughter Tia, and posted an emotional message alongside it.
He wrote: 'Thank you for all you do for the little munchkins. From keeping their mums memory alive, to constantly putting smiles on their faces. Love u.'
Kate recently shared a loved-up up snap of the couple to her Instagram where she joked that her beau 'knows who the real boss is' in the caption.
Kate quit TOWIE in September 2017 to focus on becoming a stepmother.