A SPANISH man has been sentenced to 40 years in prison for killing his two children, aged six and two, to take revenge on his wife for leaving him.

Jose Breton said the children, Ruth who was the eldest and Jose, went missing on October 8, 2011, while on an outing with him at a park in the southern city of Cordoba, a month after his wife had left him and moved to another city with the two youngsters.

The 41-year-old former soldier, who has always proclaimed his innocence, was arrested ten days later on suspicion of kidnapping.

Police drained local ponds, dragged rivers and searched properties but failed to find any trace of the children.

However, the investigation which has gripped Spain took a twist in August 2012 when two forensic scientists hired by the children's mother determined that a mass of charred bones found in a homemade oven on a piece of land outside of Cordoba owned by Breton's parents belonged to a two-year-old and six-year-old child.

Police scientists had originally said the bones found in the furnace belonged to animals.

Forensics experts determined that the children were given tranquilisers but could not say if they were still alive when they were incinerated in the oven.

The trial jury, made up of seven women and two men, found Breton guilty of murdering his young children on July 12. On Monday, a Cordoba court gave him a jail sentence of 40 years -- twenty years for each murder.

"The accused conceived of the idea of killing the children as revenge against his spouse," the court wrote in its ruling.