Harry Potter, The Chosen One, was left an orphan at the age of one when Lord Voldemort murdered his parents on the night of October 31st, 1981. James Potter and Lily Evans both were 21 at the time of their deaths. If James and Lily were this young when they were murdered, it would be very safe to assume that their parents were still alive.
But that is not the case here. As we know that Lily’s sister Petunia Dursley was the closest and likely only living relative he had after being orphaned, we know that none of his grandparents are alive at this point. Very little is known about any of Harry’s grandparents, and lesser is known about the causes of their deaths.
Fleamont and Euphemia Potter
In the Potter family, Fleamont and Euphemia Potter were both pureblood and came from affluence. It is not determined when any of them were born. After his graduation, Fleamont potter developed Sleekeazy’s hair potion, and the sales of the same are believed to have quadrupled the already wealthy family’s gold. It is also not known when he got married to Euphemia. The couple was having a problem conceiving a child and had lost hope that they would ever have a son or daughter of their own.
As a fortunate and very happy surprise, in 1959, Euphemia discovered that she was pregnant and gave birth to her only son James on 27th March 1960. It is safe to assume that this took place late in the couple’s lives and therefore their son doted on a lot and this would explain James Potter’s somewhat spoiled nature.
Fleamont and Euphemia were believed to be very good and kind people considering that their son, however spoiled, was given a good upbringing and was a good wizard who fought with the Order of the Phoenix in the war. When Sirius Black, James’ best friend left home at the age of 16, the Potters took him in as their own. Even after Sirius moved out of their house, he was always welcomed there and kept in touch with them.
Shortly after James’s marriage to Lily Evans, Euphemia and Fleamont both succumbed to Dragon Pox around 1978-1979. This means that they never got to meet their grandson who was born on 31st July 1980. The couple lived a good and comfortable life, owing to the family’s wealth, and died happily.
Mr. and Mrs. Evans
Lesser is known about Lily’s parents than about James’. Mr. and Mrs. Evans were muggles and had two daughters. Their older daughter Petunia was born sometime before 1960 and was a muggle like her parents. Lily Potter, their younger daughter, was born on 30th January 1960 and was a muggle-born witch who attended Hogwarts School of Witchcraft and Wizardry from 1971 to 1978. Petunia once stated that her parents were really happy and proud to have a witch in the family and for that, they favored Lily more and constantly talked about her, and this made the relationship between the sisters very strained.
It was stated that the Evanses died “normal muggle deaths”. In 1971, they saw Lily off to Hogwarts at Platform 9 ¾. In 1981, Lily was murdered and we know that by this point, they are both dead. This is because, if any of them was alive, Harry would have been raised by them (he had to be closely in touch with one of Lily’s blood relatives) but this was not the case. Therefore, we know that they died sometime between 1971 and 1981. Although it is more likely that they died after Lily graduated Hogwarts because nothing is mentioned of Lily living with another relative through the course of her education in Hogwarts.
It is unusual that they died in this timeframe because Lily and Petunia were still young at this point and this makes their demise untimely. The phrase “normal muggle deaths” is also ambiguous as they definitely didn’t die of old age. So was it because of a terminal illness, heart attack, car accident? It may be any of these but it also may not be a normal muggle death.
Lily and James Potter both actively participated in the war against Voldemort. This meant that they were very much on the radar of Voldemort and his Death Eaters. There have been many instances of Death Eaters terrorizing and attacking muggles. Lily also defied Voldemort three times, Voldemort hated muggles, Lily’s parents were muggles so it is very likely that someone in Voldemort’s army was the cause of their deaths. They may have made Lily’s family a target.
If this is the case, then it would also explain the extreme and adamant hatred that Petunia holds for anything magical. Petunia was always portrayed as if she is ignorant towards everything going on but she knows more about the wizarding world than she lets on. The cause of death of Mr. and Mrs. Evans may be the death eaters or it may be anything else, we may never know.