Does anyone know the name of this old Sci Fi Animation Movie

Hey All

Wonder if any of you can assist me.
I watched an animation movie when I was a kid (1980s) and would love to watch it again.
Unfortunately I dont know the title but the plot is pretty unique. Hope this discription will help hopefully ring a bell for some of you.

I watched it in German but I’m sure it was dubbed.

The movie starts with a spaceship crashing on a unhabited planet. The only survivor is a little boy. His parents die in the crash. His only communication to the outside world is a sort of two-way radio in the shape of an egg. He also meets some bird along the way.

The plot (if I recall correctly) constantly moves between the lost boy on the planet and the rescuers who are able to chat to him via this two way radio. He obviously doesn’t know which planet he is on and this was before GPS. Both the rescuers and the boy have many adventures. In the course of the movie, the rescuers recruit an old man who himself was also once lost on a lonely planet.

Right at the end of the movie, when the find the boy, the old man dies and it turns out that the old man and the boy were the same person - they were intercepting his messages that he sent many years before.

Know it sounds a bit whacked but it was a really good story. Know it was a feature film length and definitely all animation.

Any advice would be greatly appreciated.

Les Maîtres du temps?

Aye, that’s gonna be the one… awesome flick.

ETA: Not quite as good as Laloux’s Fantastic Planet, but eminently enjoyable nonetheless.