The late Mario Oriani-Ambrosini sent messages to his closest friends before taking his own life.
MPs from across the political spectrum paid tribute to their IFP colleague in the National Assembly on Tuesday.
He took his own life at the weekend after a long battle with terminal lung cancer.
He was 53 years old.
Buthelezi spoke for the first time about the circumstances surrounding his friend's death.
"Oriani-Ambrosini sent a message to a few of his closest friends describing his physical conditions and saying farewell. He wrote, "I'm dying in peace and serenity surrounded by the love of my family and friends."
Democratic Alliance MP Wilmot James recalled his last interaction with him.
"I last saw Mario a week ago and he said he was very tired and wanted to go and sleep."
In a statement on Monday, the party said Ambrosini was in the last stages of terminal lung cancer and decided to end his long battle of suffering with a positive and very conscious decision on his part.
He had been campaigning for the legalisation of cannabis for medicinal use.