Fernando Gonzalez de Castejon, who is the 53-year-old Count of Atares and Marques of Perija, shot his 44-year-old wife called Gema as well as her 73-year-old friend before shooting himself dead.
The three dread bodies were discovered at a flat in the Salamanca district, one of the richest areas in the Spanish capital, earlier in the week.
Local media report the count’s body and the body of the elderly woman were in the living room, while his wife’s body was found in the kitchen with a shot to the head.
The wife’s body is reported to have been spotted by neighbours who then contacted the police.
Pistols, knives, military uniforms, substantial quantities of ammunition and other military gear were unearthed by police after the incident.
Spanish press reported Gonzalez de Castejon perpetrated domestic abuse against his wife during their marriage.
Police have said the aristocrat, who was known as the count by local residents, did not have a licence for the weapons arsenal discovered at his home.
Data shows some 1,150 women have been killed by their partners or former partners in Spain since 2003 when they first started recording these statistics. A number of killings of women have provoked fury in Spain in recent years, with protesters marching to show their opposition to femicides.