Chilling moment gym teacher leading a fitness class for seniors is executed in a hail of bullets

Harrowing video shows the moment a gunman approached a gym teacher leading a group of seniors in Brazil and executed him at close range.

Diego dos Santos, 33, was teaching a physical education class in Esperança Nova, Paraná, on Tuesday when the chilling murder occurred.

In surveillance video, the assailant can be seen walking toward dos Santos as he speaks with a colleague before raising a gun and shooting the teacher.

After dos Santos falls to the ground, the gunman continues to discharge the weapon - firing at least 15 shots at the man before fleeing.

Dos Santos was pronounced dead on the scene. The gunman has not been identified.

Diego dos Santos, seen here with his fiancée, was shot dead at the gym where he taught classes to senior and children in Esperança Nova, Brazil on Tuesday. Dos Santos has just learned Tuesday that his wife-to-be was two months pregnant

Surveillance footage shows the gunman approaching dos Santos and aiming his gun

At least 15 elderly people were inside the gym at the time of the shooting, but none were harmed. Some were so shaken that they were taken to a local medical facility for treatment, Brazilian news outlet G1 reported.

Dos Santos' murder came just one day after he learned his fiancée, Ingrid Carbonera, was two months pregnant. He also had a son from a previous relationship.

Military Police said the suspect followed dos Santos on his motorcycle from the nearby town of Pérola to Esperança Nova. Surveillance footage shows the assailant entering the gym just after dos Santos.

Dos Santos' mother, Fatima Callegario, is running for the Esperança Nova city council, but police have ruled out politics as a motive.

The body of Diego dos Santos is loaded into a medical examiner's truck outside the gym where he was shot dead Tuesday

Diego dos Santos had planned to marry his fiancée, Ingrid Carbonera, in December

Authorities have been looking into whether the murder was the result of a love triangle.

Dos Santos had been the sports director for the Esperança Nova City Hall for two years and taught gym classes to about 40 seniors and 60 children.

'He was an admirable person, whose life touched everyone who had the privilege of knowing him,' Esperança Nova City Hall said in a statement. 'His departure leaves an irreparable gap in our lives and in our hearts.'

Dos Santos played futsal and coached a youth soccer team in his spare time.

'Since he was a child, he was very competitive,' his former school teacher, Cezar Pondian, said. 'He didn't like to lose, he was very competitive and he also took this to his athletes, as a teacher with a lot of determination and a lot of grit.'