President Mnangagwa has sent a message of condolence to the Marufu family following the death of Ambuya Idah Marufu, mother to former First Lady Grace Mugabe and mother-in-law to former president Mr Robert Mugabe.
Ambuya Marufu died at the Trauma Centre on Thursday evening.
She was 83.
In his condolence message, President Mnangagwa said he had learnt of her death with sadness as it came at a time when the former First Lady and her husband were not well.
"I learnt with sadness of the death last night of Ambuya Marufu, mother to our former First Lady, Amai Grace Mugabe, and mother-in-law to our former president Cde R. G. Mugabe," he said.
"This sorrowful development visits us at a time when the Mugabes are not well, with Amai Mugabe away in Singapore where she has been receiving medical attention.
"My heart goes out to the family. I urge our entire nation to stand with, and rally behind the Marufu and Mugabe families so their sorrows are assuaged and made bearable.
"On behalf of the party, zanu-pf, Government, the Mnangagwa family, and on my own behalf, I wish to express my deepest condolences to the Marufu and Mugabe families on this their saddest loss.
"May they derive comfort from the broad support which the nation continues to give them during this hour of deep sorrow and grief."
Mrs Junion Shuvai Gumbochuma, sister to Mrs Mugabe, attributed her mother's death to old age.
"She died yesterday (Thursday) evening and she was not ill at all," she said.
"We attribute her death to old age and she has never been in hospital all the time except taking tablets for problems like BP. Maybe in the long run those tablets can cause problems.
"As a family, we have lost a pillar and unifier. She was a loving mother and did not want any fights in the family. This is a great loss to us. She is irreplaceable, meaning the void left will be difficult to fill.
"We are still working on the burial arrangements and we will notify you when we have an agreed position."
Mrs Marufu is survived by four children - three daughters and a son - and several grandchildren and great-grandchildren.
Mourners were gathered in Pomona, Borrowdale Harare.