Prince Harry has thrown his weight behind HIV Testing Week as he handed out self-testing kits at a pop-up clinic in London.
He said the UK had "turned a corner" over public stigma around the illness and encouraged the knowledge that people with HIV could live "healthy, happy lives".
Harry met volunteers and employees from the Terrence Higgins Trust, which is behind the week-long placement of the testing centre in Homerton, east London, and heard how a simple finger-prick test can determine whether someone is HIV positive in less than 15 minutes.
As he watched the face of the "Give the finger to HIV" campaign, Yvette Twagiramariya, explain the workings of the clinic, Harry said people could no longer be demonised for getting tested and are now only "irresponsible" if they do not know their status.
He said: "If you are positive, it's absolutely fine - you can have a healthy, happy life.
"Rather than not knowing your status and being on medication for a period of your life, or the rest of your life, rather than letting yourself get to that point where there is no return, I must stress to everyone how important it is (to get tested).
"The sooner the better."
Harry's visit comes two months after the 20th anniversary of his mother Princess Diana's death in August 1997, and 30 years since she was first credited for challenging the stigma against those afflicted by the virus.
At the opening of the UK's first purpose-built HIV/Aids unit that cared exclusively for those suffering with the disease, the 25-year-old Princess shook hands with an Aids patient without wearing gloves - dispelling myths that it could be passed from person to person by touch.
On Wednesday, Harry sat with Andrew Bates, who was found to be HIV positive in 2015 and spoke to the Prince about the process of being diagnosed.
Harry heard that despite his initial fears about the impact of the disease, Mr Bates is under daily treatment that keeps his symptoms at bay and is now planning to run a marathon next year to raise awareness about the lives of those who are on HIV medication.
Mr Bates said: "I want to say that people who are HIV positive can do things like run a marathon - just because I have this diagnosis, it doesn't define me."
He added: "I was told at the time I was diagnosed that in six months, I would laugh at my reaction - those initial feelings of shock and upset, and that is it. You will look back and see that it is fine."
Harry then took the opportunity to get stuck in with other Terrence Higgins Trust volunteers by handing out self-testing kits to residents in the local Hackney area.
The Prince asked one resident if he would be encouraging friends to visit the clinic and asked others to spread the word about the ease of coming to get tested.
Last year, Harry had his own high-profile HIV test alongside pop-superstar Rihanna while on a visit to Barbados, demonstrating his commitment to breaking down the fears surrounding the disease in the same way that his mother did 30 years before him.