Royal Biographer Angela Levin defended Prince William for “doing his best” as the Prince of Wales stepped out for his first public engagement since the news of Princess Kate’s cancer. William visited food charity Surplus to Supper in Surrey earlier this week, as the royal leant a hand in preparing and delivering goods to a youth centre in Feltham. The appearance came after the Princess of Wales announced her cancer diagnosis last month, following an abdominal procedure in January. William was said to be “touched” during his visit after a volunteer gifted him two get well soon cards, one for Ki…