Nope, not an illegal imitation. The Spanish Bruguera publishing company bought in 1968 the rights of “Les Aventures de Tanguy et Laverdure” among other Franco-Belgian cartoons and they used their “Revista Juvenil Bravo” magazine to distribute them in Spain. As an aside, the Spanish Ejército del Aire (AF) bought later the real deal.
The artist of this very decent cover was Edmond (Edmond Fernández Ripoll). A few of these old “tebeos” were, gladly, still at hand when I was a kid. Happy times.