Read this: In 1870, republican sentiment in Britain, fed by the Queen's seclusion, was boosted after the establishment of the Third French Republic. A republican rally in Trafalgar Square demanded Victoria's removal, and Radical MPs spoke against her. In August and September 1871, she was seriously ill with an abscess in her arm, which Joseph Lister successfully lanced and treated with his new antiseptic carbolic acid spray. In late November 1871, at the height of the republican movement, the Prince of Wales contracted typhoid fever, the disease that was believed to have killed his father, and Victoria was fearful her son would die. As the tenth anniversary of her husband's death approached, her son's condition grew no better, and Victoria's distress continued. To general rejoicing, he pulled through. Mother and son attended a public parade through London and a grand service of thanksgiving in St Paul's Cathedral on 27 February 1872, and republican feeling subsided.

After what event did the Prince of Wales' health begin to improve?
What is the answer? (If it cannot be answered, return "unanswerable")
the tenth anniversary of her husband's death