Joe Biden recently had surgery to remove cancerous cells from his skin, a spokesman for the former US president has confirmed.
The skin cancer scare comes as Mr Biden, 82, has been undergoing treatment for an "aggressive" form of prostate cancer.
A spokesman for the Democrat revealed the prostate cancer diagnosis in May after a small lump was found during a routine physical examination.
His office told NBC News on Thursday that he had since also undergone Mohs surgery, a procedure which removes layers of skin containing cancer cells. Mr Biden was said to be "recovering well".
It is unclear when the former president underwent surgery, although public appearances suggest it was in the past month.
Mr Biden was pictured earlier this week leaving a church in Delaware with a large scar on his forehead.
In August, he was seen wearing a bandage over his head while attending the funeral of Mike Castle, a former Delaware governor.
Performed under local anaesthetic, Mohs surgery is the "gold standard" for treating many basal cell carcinomas (BCC) and squamous cell carcinomas (SCC), according to the Skin Cancer Foundation which notes the procedure targets cells in "cosmetically and functionally important areas around the eyes, nose, lips, ears, scalp, fingers, toes or genitals".
"Mohs is also recommended for BCCs or SCCs that are large, aggressive or growing rapidly, that have indistinct edges, or have recurred after previous treatment," the foundation states on its website. "Some surgeons are also successfully using Mohs surgery on certain cases of melanoma."
Mr Biden and his wife, Dr Jill Biden, have previously been treated for skin cancer.
In 2023, while Mr Biden was president, he had a lesion removed from his chest during a routine physical examination. A biopsy revealed the lesion was BCC, a common form of skin cancer. Doctors also found BCC growths above the then First Lady's eye and on her chest.
At the time, Dr Kevin O'Connor, Mr Biden's physician, said in a memo on the president's health that "all cancerous tissue was successfully removed" and that "no further treatment is required".
In May, Mr Biden's office announced that his prostate cancer had spread to the bone.
"Last week, president Joe Biden was seen for a new finding of a prostate nodule after experiencing increasing urinary symptoms," a spokesman said.
"On Friday, he was diagnosed with prostate cancer, characterised by a Gleason score of 9 (Grade Group 5) with metastasis to the bone."
He added: "While this represents a more aggressive form of the disease, the cancer appears to be hormone-sensitive, which allows for effective management.
"The president and his family are reviewing treatment options with his physicians."
Mr Biden then posted an image of himself and Dr Biden, which read: "Cancer touches us all. Like so many of you, Jill and I have learnt that we are strongest in the broken places. Thank you for lifting us up with love and support."
Responding to the news, Donald Trump said: "Melania and I are saddened to hear about Joe Biden's recent medical diagnosis.
"We extend our warmest and best wishes to Jill and the family, and we wish Joe a fast and successful recovery."
Sir Keir Starmer said at the time that he wished Mr Biden a "swift and successful treatment".