Ozzy Osbourne may have been the guest of Fox News Channel's Greta Van Susteren at this year's White House Correspondents' dinner -- but that isn't stopping him from threatening legal action against her network. The rocker-turned-TV dad and his lawyers are trying to block the network from airing Susteren's one-on-one interview with Ozzy tonight; in it, he talks candidly about his wife's cancer and his hit MTV series. The reason for his change of heart? According to the New York Post, Ozzy had already agreed to give an "exclusive" interview to ABC's Barbara Walters. Lawyers for the MTV star claim Osbourne only agreed to discuss the 25th anniversary of Elvis Presley's death for Van Susteren's news show, "On the Record." "This interview was conducted under false pretenses, in violation of our clients' legal rights and contrary to established journalistic standards and is being falsely advertised," his lawyers wrote in a letter to Fox, obtained by the Washington Post. For its part, Fox News Channel denies any wrongdoing, pointing out to the Post that Osbourne talked for nearly one hour -- and Van Susteren asked just one question about Elvis. The interview is expected to air as scheduled Friday at 10 p.m.