Heaven And Hell's appearance at Classic Rock's High Voltage festival in London later this month will be the band's final appearance, following the death of singer Ronnie James Dio in May.
Iommi, Geezer Butler and Vinny Appice later announced they'd perform a tribute set at High Voltage with Glenn Hughes and Jorn Lande singing in Dio's place.
That's led to speculation about some kind of tribute tour but Iommi says the London show is a one off, and they didn't even expect to do that.
The guitar hero tells Classic Rock: "We didn't expect to be playing again. It's certainly going to be a strange feeling but we thought it would be nice to do one final thing for Ronnie.
"It's going to be the only one. I suppose it would have been good for other people to see it. But this is something we need to do for ourselves as well."
High Voltage takes place in Victoria Park on July 24-25 and stars ZZ Top, ELP, Foreigner, Joe Elliott and Ian Hunter, Black Label Society, Down, Marillion and many more.
Thanks for the report to RockRadio.