King Albert II of Belgium has kickstarted cancer treatment for the sixth time in 11 years.

The 91-year-old former monarch, who stepped down from the Belgian throne in 2013, is once more undergoing preventative treatment for skin cancer, according to a statement by the Belgian Royal House to Dutch outlet Het Laatste Nieuws.

The palace confirmed that Albert had the procedure, though did not specify when the surgery took place.

The outlet had published an image of the former king attending a reception in Brussels last week, revealing a visible scar running from his nose to his upper lip following the recent procedure.

The rare outing marked his first in five months.

Albert has previously been treated for cancer on 10 occasions, with medical experts suggesting that his condition may have been triggered by frequent sun exposure during his travels abroad.

In 2013, he was hospitalized with signs of dehydration.

At the time, the palace said that Albert had been “admitted to hospital as a precautionary measure. Examinations are being done. He is conscious.”

The health scare prompted Albert to abdicate the throne in July of that year — handing the crown to his son, King Philippe, 65.

The abdication effectively ended his 20-year reign.

Albert — who is the third and youngest child of King Leopold III — became king in 1993 after taking over the crown from his brother Baudouin, who died without children.

Speaking to the BBC at the time of his abdication, Albert said, “I realize that my age and my health are no longer allowing me to carry out my duties as I would like to. Prince Philippe is well prepared to succeed me.”

Following his diagnosis, Albert and his wife, Queen Paola, 85, have been spacing out their public appearances.

Following Albert’s most recent surgery, King Philippe had reportedly canceled his planned royal engagement at the University of Ghent so that he could visit his father in the hospital.

Other members of the Belgian royal family, including Prince Laurent and aspiring DJ Prince Emmanuel, had also visited the Saint-Luc hospital in Brussels.