When Karna was dead and about to be cremated, Duryodhana said that only he owns the right to light fire to Karna’s body.
Yudhisthira walks to Duryodhana and says that Karna is the eldest Kunti Putra and being the second eldest brother, he only owns the right to cremate him.
To this Duryodhana had said
This is not the dead body of eldest Kunti putra. This is the dead body of my best friend who died for me in the battlefield. Ask Vasudeva Krishna, is this the dead body of eldest kunti putra or is this the dead body of my best friend?
Krishna said that Duryodhana is right and he has the highest right over him. Hence, Karna’s final ceremony was performed by Duryodhana and not Yudhisthir.