The rocker and the actress have joined forces to urge the Prime Minister to address the issue at the upcoming G7 summit in a new letter.
"We face a new AIDS emergency, and we need your help," the letter begins. "While naturally COVID-19 is currently dominating the agenda, it is vital that you and your fellow leaders also protect and build on what we have achieved in the fight to end AIDS and use that in the struggle against COVID-19."
"The COVID-19 crisis has shut down HIV prevention and treatment services, in many countries literally overnight. It has cut off millions of girls from school, and driven up poverty, gender-based violence and human rights violations. All of these factors increase people's risks of acquiring HIV or of developing AIDS. Already we have seen a steep increase in rates of adolescent pregnancy, which we know will mean a surge in HIV infections too."
The letter also points out that officials behind the Global Fund for AIDS, Tuberculosis and Malaria have warned that HIV service delivery has been massively disrupted with HIV testing falling by 41 per cent across 502 health facilities in Africa and Asia, and the World Health Organization has highlighted widespread disruption to HIV treatment supply chains.
Both stars have big ties to the AIDS issue - Theron is the founder of Charlize Theron Africa Outreach Project, while Sir Elton is the brains behind the Elton John AIDS Foundation.
"As leaders and champions of the global HIV response, we now fear that the number of new HIV infections and AIDS-related deaths will climb again," their letter reads.
The G7 meeting in June comes as AIDS activists mark the 40th anniversary of the first cases.
"The G7 must commit to increased investment in tackling long-standing, new and future pandemics together," the pair write. "The U.K. must drive ambitious G7 support for international progress as convenor and by example. The eyes of the world, Prime Minister, are on the U.K., and on you."