Paul Jubb, who was given a wildcard entry to Wimbledon after winning a tournament open to the best youngsters in America, will play on Tuesday against Portugal’s Joao Sousa.
Jubb's father Sean, a former soldier, took his own life in January 2000 when he was 30 and mother Jacinta died in hospital in 2008.
After years of raising him by herself, Jubb said it will be a nice moment when he makes his debut with his grandmother Valerie watching on.
“It’s going to be a great experience for me, I’ve just got to go there and do the best I can and just compete really hard and take it all in,” he told ITV News.
“She [his grandmother] has raised me since I was a little kid so it’s just a nice moment we can have.
"She’s been a hero to me and I love her so much.”
Valerie told ITV News the only hardship the teenager had to face was picking between the sports he wanted to play.
She said: “It was impossible. We were playing football on a Saturday morning, we were going to tennis Saturday afternoon.
"Tennis Sunday some time, so he had the choice.
“Tennis or football, I said take your pick because we cannot do both.”
His talent for tennis was spotted by coaches from the University of South Carolina which gave him a scholarship.
And, in May, he became the first Brit to win the National Collegiate Athletic Association men's singles title in the US.
His grandmother added: “His dad and his mum would be proud. My other three grandsons, they’re all proud of him, all the family’s proud of him.”
Had he been American, his May tournament win would have earned him a wildcard into the US Open as well.
But Jubb, ranked 579 in the world, will be unable to collect the guaranteed £45,000 in Wimbledon prize money, because he plans to stay as an amateur and complete his final year at the University of South Carolina.
All England Club chief executive Richard Lewis said: "It's a great story, isn't it?
"Great credit to him as an individual, fantastic what he's done, it was great to be able to give him a wild card, I think it was thoroughly deserved what he achieved.
"It will be fascinating to see how he plays.
"It's a big stage but every sign is he's got a great temperament and he certainly deserves this opportunity."