Wiktionary
interj. (context idiomatic English) To say that one hopes that something does not happen.
Wikipedia
Heaven Forbid is the thirteenth studio album by the American hard rock band Blue Öyster Cult, released in 1998. It was the band's first studio album with new material in a decade (not counting the 1992 soundtrack to Bad Channels). American science fiction and horror writer John Shirley wrote lyrics for several songs on the album. While he is a noted author for his cyberpunk stories, many of the lyrics on this album revolve around early science fiction and mystery motifs. The album's working title was 'Ezekiel's Wheel', after the Biblical story that some take to reference an early visitation by UFOs.
A number of songs on this album have ties to previous songs released within the circle of Blue Öyster Cult. "In Thee" was originally featured on Mirrors. "Still Burnin'" is a sequel to the song " Burnin' for You" that appeared on Fire of Unknown Origin.
The inspiration for the alternative cover is Morgan Fairchild. This image also appears on the reverse of the insert, and was originally intended to be the front piece as indicated by advertisements from the period.
Usage examples of "heaven forbid".
You don't look very well at all, as though, Heaven forbid, you've a crisis of the liver.
Sleeping under a leaking sky is not for a noble lady, Heaven forbid!