According to Barbara Anderson's article at Watchtower Documents, it's been about 120 years now: (emphasis mine)
From all accounts, the Russells were a happy couple until the early 1890s. Mrs. Russell left her husband in November 1897 and they divorced in 1906. After the divorce Pastor Russell publicly distorted the facts regarding the cause of the breakup of his marriage. He denied all charges and explained that his wife left him because of revenge because he refused to permit her to take control of their religious journal to spread her women’s rights ideas. He publicly doubted his wife’s writing ability. Mrs. Russell asserted that she did at least half of the writing for each one of the first four volumes of the Millennial Dawn series of books; yet, her participation has been denied. Moreover, the legal corporation she co-founded published over 50,000 pages of material which directors have given credit solely to Pastor Russell as author of.