Charles and his wife, Camilla, duchess of Cornwall, toured King's Hospital in the Camberwell neighborhood, Hello! Magazine reported.
Sir William Gilliat, the queen's obstetrician, was on staff at King's.
"My darling wife was born here, but amazingly we had the same gynecologist and nurse," Charles told employees.
The couple visited the neo-natal ward, where Camilla was a big hit with babies and parents.
"Camilla was fantastic," Amy Bernadout, whose 5-month-old son is a King's patient, told the magazine. "She had Jessie in fits of giggles and was so good with him, pulling funny faces to make him laugh. She's a gran herself, so she's obviously good with babies."
Camilla has two children and five grandchildren from her first marriage. Charles became a grandfather for the first time last year.