The 58-year-old suffered a heart attack at home in May and was rushed to hospital. He was given a 'slim chance' of survival by doctors at the Royal Devon and Exeter Hospital but following emergency surgery he has been allowed to return home.
He is now said to be 'doing much better' and wants to 'get on with his life.'
A source told the Mirror: "He's glad to be out as he has had enough of being in hospital. He is doing much better but still needs to build up his strength. Now he just wants to put this behind him and get on with his life."
The ex-Army officer has now returned to the home he shares with his mother in a former country house near Exeter, Devon.
Hewitt had a five-year affair with Diana while she was married to Prince Charles. After the affair became public in 1991 he served in the Gulf War.
In March, Hewitt appeared on Australian Channel Seven's Sunday Night. Speaking candidly from his home in the southwest, he broke his long-held silence on their affair.
The royal reportedly embarked on an illicit relationship with the former army officer in 1986, after she asked him to be her horse riding instructor.
He said he had no regrets about their time together. "No, I don't regret that. I regret some of the things that have been caused by that but not that at all. No way," he said.
He added: "I think she was quite easy to fall in love with really so I think I can be forgiven for that."