By Martin Fricker King Charles made a show of smiling and waving to well-wishers as he walked to church yesterday, a few days after his cancer diagnosis. The monarch, who gave his “heartfelt thanks” for messages of support on Saturday, was joined by the Queen for the service at Sandringham. Charles, 75, appeared in good spirits as he strolled at his usual brisk space to St Mary Magdalene Church on the Norfolk estate. Sources close to the King say he is “keen to be seen” as he undergoes treatment for unspecified cancer. More than 100 fans gathered to watch him walk from Sandringham house to the…