The Local newspaper said Daniel Westling's operation wasn't announced in advance. The newspaper also said it wasn't publicly known until this week that he suffered from a congenital disorder that led to impaired kidney function.
"Daniel Westling has today undergone a kidney transplant at Karolinska Hospital and he is doing very well," Nina Eldh, spokeswoman for the Royal Court, told the Swedish news agency Tidningarnas Telegrambyra..
Eldh added Westling's father, Olle, is also recovering nicely after undergoing surgery to remove his kidney.
Westling and the princess are set to wed June 19, 2010.