The two fathers of democratic South Africa disagreeing - albeit in jest - about Houston is unimaginable, considering the weighty matters of national importance that they grappled with in their everyday lives.
But in remembering her late friend - who was found dead at the Beverly Hills Hotel in Los Angeles on Saturday - Mandela's daughter Zinzi told Sowetan how much Houston came to be a factor in hers and her family's lives.
She recalled that when Houston performed in SA in 1994, Sisulu demanded to attend the concert.
Zinzi was part of the team that had arranged the tour.
"Tata Sisulu told my father that he did not understand why all the attention was on him when they all knew he (Sisulu) was the number one fan," said Zinzi.
"He boasted how he knew all her songs."
She said her family struck up a warm relationship with Houston's family after 1990 and they had even spent Christmas holidays together.
Zinzi said her mother, Winnie Madikizela-Mandela, and Houston's mother, Cissy, had a close relationship.
"We may not attend the funeral but mama will phone her (Whitney's) mother.
"I plan to visit the family after the funeral because that is the crucial time when family needs support," she said.
She added that both families had gotten much closer after Houston's 1994 concert in Johannesburg.
"My heart is broken. Whitney was such a humble person. She was comfortable in any space."
Zinzi recalled how she dedicated her song The Greatest Love of All in 1994 at the White House where her father was hosted by former US president Bill Clinton.
She also dedicated her other song, Me Against the World, to her and Madikizela-Mandela.
"Tata was worried at the time about how thin she was and how she got into such a tight dress without a zip. I guess he did not understand the stretch material."
Zinzi also recalled how the Mandelas and Houstons exchanged gifts .
"We gave the Houston family blankets, doeks and a walking stick for Bobby Brown (her singer ex-husband) but when we visited them we got designer clothes."
She said whatever happened to Houston, including her marriage, was unfortunate.
"Her and Bobby's was a spiritual relationship. They loved each other.
"Bobby is a real township boy and that's what she loved about him," she said.
Meanwhile Houston's funeral will be held on Saturday in the church where she first showcased her singing talents as a child, her family choosing to remember her in a private service rather than in a large event at an arena.