Step 1: ``My grandfather'' refers to Sihiti’s grandfather.
Step 2: ``My son of my grandfather'' means the son of the grandfather, i.e., Sihiti’s father.
Step 3: ``The only son of my father'' refers to Sihiti himself.
Step 4: ``The son of me'' means Sihiti’s son.
Step 5: However, since Sihiti is pointing to a person of the same generation and the only son condition applies to the father, the statement logically resolves to the person being Sihiti’s brother.