Baby Maxim Sagalakov was left by his mother Viktoria, 20, in the care of her parents in the Khakassia district of .
When she returned, the distraught woman found the child's charred remains in the stove of the family's house in Kharoy village.
'The grandparents were drunk and killed the baby,' said a statement from the regional Investigative Committee in charge of probing serious crime.
'A family member found the body of the boy badly damaged by the high temperature inside the stove.'
The exact cause of death is under forensic investigation but it is believed the child died from incineration after being burned alive on Tuesday.
A neighbour said the grandfather had been out and got drunk on vodka.
When he returned the child was thrown into the stove.
The grandmother, 42, and grandfather, 47, who's surname is Miyagashev, have both been arrested and a criminal investigation has been launched into the 'deliberate murder of a helpless minor', said law enforcement sources.
Mother Viktoria Sagalakova, 20, left an emotional message on social media.
'Rest in peace, my beloved son,' she wrote. 'My dear little son. My pain does not ease even for a minute.
'How will I cope with it that you are not with me? I can't hug you. Only your photograph is here with your kind and tender look.
Dailymail