Spanish TV presenter Sara Carbonero announced on Instagram that she has undergone surgery to remove a malignant ovarian tumour and will have further treatment in the next coming months.
She wrote: "When we had not yet recovered from a scare, life has surprised us again. This time it has touched me, that damned six letter word that I still have trouble writing.
"A few days ago, in a regular checkup, doctors found a malignant ovarian tumour and I have already had surgery. Everything has gone very well. Fortunately, we have caught it in time but I still have a few months of struggle while I continue the necessary treatment.
"I am calm and confident that everything will turn out well. I know that the road will be hard but also that it will have a happy ending. I count on the support of my family and friends and a great medical team."
Casillas had suffered a heart attack while training with Porto on May 1 and was discharged five days later.
Porto expect Casillas to make a full recovery but the former Real Madrid and Spain captain has not made a decision regarding his playing future.
He turned 38 on Monday and celebrated by posting a photograph on Twitter with the message: "It hasn't been a great birthday. At least, I didn't give it the attention I should have!
"Still, I have posed and shown my face. Happy despite having been here for 20 days now! 37 [years] have gone... finally! Welcome 38!"
Casillas and Carbonero met before the 2010 World Cup and have two boys aged five and two.