Two weeks later on August 26, Viacom acquired Warner Communications and Warner-Amex's combined 50% ownership interest in Showtime/The Movie Channel, Inc. as well as full ownership of the Warner-Amex and public shareholder interests in MTV Networks for $671.7 million, giving Viacom exclusive ownership of both networks and once again making it the sole owner of Showtime through its $500 million cash payment and acquisition of 1.625 million shares from Warner for the latter's 31% stake in Showtime/The Movie Channel and Warner-Amex's 19% interest in the unit and its 60% interest in MTV Networks (Viacom owned Showtime alone or jointly with other companies – TelePrompTer Corporation, and later briefly, its successor Group W Cable – from the time it launched in July 1976). The buyout, part of an option given by Warner in its purchase of American Express' interest in MTV, was exercised in part to finance much of the buyout of Showtime/The Movie Channel without borrowing any money (ironically, Warner Communications would eventually acquire rivals HBO and Cinemax, when the company merged with Time Inc. in 1989 to form Time Warner). The subsidiary was renamed Showtime Networks, Inc. in 1988.