Former glamour model Katie shared two snaps of her 12-year-old boy, who was performing on stage inside the Royal Festival Hall at the Southbank Centre in London.
She said: "So proud of my Harvey tonight playing the piano at Royal Festival Hall #proudmum."
She later added: "Harvey is absolutely amazing love him so much xxxx."
Last week, Harvey won the hearts of the nation as he joined his mum and nan Amy on the sofa for ITV's This Morning.
Katie openly spoke about the struggles and joys of raising her eldest son Harvey, who has multiple disabilities including Prader-Willi Syndome and autism.
"To other people, they say, 'Oh my God, how do you cope?' But I don't know any different," she said. "It is hard work."
As Katie turned to Harvey, she said: "You do play up to mummy sometimes, don't you?"
He replied: "Yeah, babe!"
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