Ndaba Mandela was at home in Johannesburg with friends on Saturday when he received a call that shook him to the core: he had tested positive for Covid-19.

Mandela, the grandson of former president Nelson Mandela, arrived back in SA from New York last Sunday - the same night President Cyril Ramaphosa addressed the nation and declared a state of disaster over the coronavirus and Covid-19, the respiratory illness it causes.

The following day, Mandela went to get tested because he had returned from the US, which is officially listed as a high-risk country.

Listen to what he had to say: 

"I got the actual result on Saturday night. At the time I was at home with friends, taking it easy, not doing anything crazy. My world stopped for a second. I went into a room by myself and my heart, I got a little bit of heart palpitations," he told SowetanLIVE's sister publication TimesLIVE.

"Basically the world stopped and I was like, 'What the hell?'"

He said from sheer stress, he did one of the worst things possible.

"I guess in that moment I just started smoking more cigarettes, which was honestly the worst thing to do. You need to actually protect your chest more than anything because it [Covid-19] does end up affecting your respiratory system and your lungs," he said.

Fortunately, he said he was feeling OK.

"I haven't really had any symptoms, thank God," he said.

Mandela took to Instagram on Sunday to share his positive diagnosis, and said he had received a lot of support in response.

The most difficult part, he said, was not seeing his children.

"When I went to be tested on Monday, the doctor told me to stay away from my children. The doctor told me to go into quarantine for 14 days. Of course the most difficult thing during this period has been not seeing my kids. We've been FaceTiming, but you know that's not enough. My son is obviously very, very sad that he hasn't been able to see his dad.

"The most important thing is to let people know to stay calm, that this disease is not a death sentence, that you can actually fight the disease - and you can win.

"I am a born soldier and I have had to fight all my life with different things. This is just another one of those hurdles we must go through."

Mandela also offered advice to those who get the illness and those scared of contracting it.

"The most important thing is that you wash your hands consistently. It's important, whether you have the disease or not, to eat very healthy. And that you don't consume alcohol because alcohol reduces the strength of the immune system," he said.

Mandela said tea made with hot water, ginger, garlic, turmeric and honey can "really help your immune system".

The tea will not, however, make you immune to the coronavirus.