Pope Francis is currently in hospital suffering from a complex infection in his respiratory system, prompting doctors to administer a more targeted treatment.
Officials say the 88-year-old pontiff has a "polymicrobial respiratory tract infection", but little remains known about the severity of his illness.
Here's a look at the pope's latest diagnosis and what might happen next should he retire.
What is a polymicrobial respiratory tract infection?
In basic terms, it means there's a mix of bacteria, viruses, fungi or parasites growing in someone's lungs.
While a bacterial infection can be treated with antibiotics, viral infections cannot.
Viruses usually have to run their course, but the patient can be assisted with other medicines to bring down their fever or help their body fight the infection.
Such issues can be common in older people whose immune systems might be weaker or who have complex health issues.
"All tests conducted up to today are indicative of a complex clinical picture that will require an appropriate hospital stay," the Vatican said.
How serious is this?
Pope Francis's hospitalisation can be worrying when viewed in the context of his previous medical history.
The pope lost part of his right lung decades ago and has previously had pneumonia.
Dr Nick Hopkinson, medical director of Asthma + Lung UK, told the Associated Press most healthy people would likely recover quickly from bronchitis.
But in people whose lungs were already damaged, "bacteria can come and colonise the airways … and you start to see infections, which makes it more difficult to treat".
In people with lungs that have been previously compromised, they might need help breathing, including oxygen support or chest physiotherapy to help them clear fluids building up in their lungs.
The Vatican has provided updates on the pope's condition, saying he is "stable" with no fever, but will remain in hospital for as long as necessary.
What has Pope Francis's health been like recently?
The pope has suffered a number of medical setbacks in recent months, including a fall last month at his Santa Marta residence where he hurt his right arm.
A separate fall in December led to a visible bruise on his chin after he collided with a night stand.
Would Pope Francis retire? Can he even do that?
It is incredibly rare for a pope to retire, but it has happened before.
In 2013, Pope Benedict XVI shocked not just the Catholic community but the world when he announced his decision to step down, saying he no longer had the "strength of mind or body" to carry on.
Pope Benedict died on December 31, 2022.
After leaving the leadership, his title changed to Pope Emeritus.
The only other pope in history who resigned by choice was Celestine V, who stepped down in 1294 after just a few months in office.
Earlier, Vatican spokesperson Matteo Brunit said Pope Francis was in "good spirits".
How is a new pope chosen?
There is no family tree or line of succession when it comes to picking a new pope.
Instead, the decision is up to cardinals, who go through the process of a papal conclave to vote on who they want to take over.
Cardinals are not allowed to have any contact with anyone outside the conclave, or risk excommunication.
The 2025 film Conclave, starring Ralph Fiennes, Stanley Tucci and Isabella Rossellini, gives viewers an insight into the ancient and secretive process.
After Pope Benedict stepped down, the majority of the cardinals' vote went to the Archbishop of Buenos Aires, Cardinal Jorge Mario Bergoglio, who we now know as Pope Francis.
In an interview with a Spanish newspaper, Pope Francis revealed that, shortly after he was elected, he wrote a resignation letter to have on hand in case medical problems impede him from carrying out his duties.
"I signed it and said, 'If I should become impaired for medical reasons or whatever, here is my renunciation. Here you have it,'" the pope said.
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