Episode 11 of The Trigan Empire
The Three Aliens
aka The Luminous Spheres
The Alien Invasion (The Collection)
De lichtende bollen (Dutch title)
The Luminous Orbs (Dutch title, translated)
A Tale of Invasion (Hawk reprint)
Written by Mike Butterworth
Illustrated by Don Lawrence
It was reprinted in 1975 in Vulcan comic.
It was reprinted in 1989 as A Tale of Invasion in Tales from the Trigan Empire (Hawk).
It is reprinted in Volume 3 of The Trigan Empire—The Collection (the Don Lawrence Collection).
It is reprinted in Volume 1 of The Rise and Fall of the Trigan Empire (Rebellion).
Plot summary (Dutch)
MediaFire via British Comics Compilations