I only have a few details, starting from the name, which could sound like Gandar. It was a short title, and it was the name of the main character.
I watched this movie in Italy, on the national channel, in the 70s, maybe early 80s, but it could be older. It wasn't Italian, and I watched it dubbed. I think it was a Western animation movie, not an Asian one, but I'm not sure about it.
It was a science fiction story, with this kid forced to leave his family for some reason. It reminds me of Superman origins, with his parents putting him in a small spaceship and sending him away, but I might have mixed another story in this, don't take it for granted. His father was a scientist, or a politician, about that I'm sure, and he struggles for his life. Someone wants to kill him, and they succeed in it, so our hero is an orphan.
He reaches a planet where he meets a girl, they become friends and there the feeling of a romance there, but the girl disappear. A cute alien animal joins him in his adventure, a short of a cat, and only in the end he finds out that it's the same girl he met in the beginning, which has a shape shifting power.
During his trip he meets his brother, a space pirate, who helps him to travel back in time to find their parents before they leave on the trip that will kill them. He tries to convince them to stay, but in vain.