Heavy metal icon RONNIE JAMES DIO has secretly reunited with his former Black Sabbath bandmate TONY IOMMI to write new songs for a box set project. Dio briefly replaced Ozzy Osbourne as Black Sabbath frontman in 1979, and has enjoyed working with Iommi again on material which will help celebrate his contribution to the band. He says, "There's a box set that's going to be released, called BLACK SABBATH: THE DIO YEARS. The proposal was to write a couple of songs to be included. "I have gotten together with Tony (and) we worked together for about a week in England. It went very well." But one reunion Dio insists will never happen is that of another great rock act, RAINBOW. The American singer tells Billboard.com, "I've tried to say 'No' as many times as I possibly could. If there is a Rainbow reunion it will not include me."