Conversation so far:
What is Radio Gnome Invisible trilogy by Gong?
The band, Gong's Radio Gnome Invisible trilogy, describes the adventures of Zero the Hero, the Good Witch Yoni and the Pot Head Pixies from the Planet Gong.
What was Tubular Bells in relation to Radio Gnome Invisible trilogy by Gong?
Tubular Bells is the debut studio album by English multi-instrumentalist, composer and songwriter Mike Oldfield.
Was Mike Oldfield part of Gong?
Mike Oldfield was not part of the band, Gong.
How did Flying Teapot by the band, Gong do?
What was the Gong mythology?
The Gong mythology is a humorous collection of recurring characters and allegorical themes which permeate the albums of Gong and Daevid Allen
What was the second part of the Gong Radio Gnome Invisible trilogy?
Angel's Egg is the second part of Gong Mythology.
When was Angel's Egg by Gong released?
Angels Egg is the fourth studio album by the progressive rock band Gong, released on Virgin Records in December 1973.

Question: When was the third released?
Self-contained rewrite: When was the third album in the Radio Gnome Invisible trilogy by Gong released?