The mother-of-two, who is Prince William's auntie, was pictured visiting the NSPCC Service Centre. She is not attending the christening due to its 'intimate' nature.
Sophie looked radiant as she met with staff and gave a speech wearing a cobalt blue wrap coat over a black shift dress and black knee-high boots. She accessorised with a snakeskin print clutch.
After weeks of speculation over the guest list, a spokesperson for William and Kate revealed earlier this month that the christening would be a "small, intimate affair".
"We are not giving details of the guest list at this stage," he said. "All we are saying is that it will be a small intimate affair with close family￼ and others, which include godparents."