Suzanne Plunkett/ReutersKing Charles III looked cheerful and happy Tuesday, as he carried out his first official public engagement since being diagnosed with cancer.He was accompanied by his wife, Queen Camilla, as he visited a cancer treatment center in London, England.The royal couple arrived at University College Hospital Macmillan Cancer Centre shortly after 11 a.m. in the state Bentley, a ceremonial vehicle fitted with extra large windows that Charles has been using while traveling in Londo