Kate, patron of the Rugby Football Union, donned an England Rugby scarf atop a dark blue coat to watch England take on Ireland in the Guinness Men's Six Nations on Saturday.
She was pictured chatting with injured England player Fin Baxter and Rugby Football Union President Deborah Griffin in the seats before the game.
It is the British princess's first public engagement since Andrew was arrested on Thursday on suspicion of misconduct in public office after allegations were made against him following the release of files related to paedophile billionaire Jeffrey Epstein.
The former duke spent 11 hours in police custody on his 66th birthday before being released under investigation following allegations he shared sensitive information with Epstein during his time as the UK's trade envoy.
Kate and her husband, Prince William, will have the task of rebuilding the "integrity of the royal family" damaged by Andrew's friendship with Epstein, a PR expert suggested.
Public relations and crisis consultant Mark Borkowski said the couple faced the question of "how do they establish the integrity of the royal family?"
The pressure on William to communicate what the royal family is going to be over the next 50 years falls squarely on his shoulders.
"The heavy weight of this burden on the royal family's reputation lies with William and Kate and what they're going to do," he said.
William has already said "change is on my agenda" when he comes to the throne, but he may have to open himself and the monarchy up to greater scrutiny as long-held attitudes towards the royal family die out.
The couple have been in lock-step with King Charles' decision to distance the royal family from Andrew by stripping him of his titles last year.
The king issued an emphatic statement a few hours after Andrew's arrest on Thursday, which stated: "The law must take its course".
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