The glamourous TV presenter will follow Casillas to Portugal to raise their son as Iker plays this season with Porto.
In her blog with Elle, Sara wrote: "I want to join the unanimous praise in these days that has again demonstrated his values, his strength, his poise, his generosity, humility, temperance, nobility ... One of the biggest hopes in life is to share it with someone you admire deeply. I have that luck.
"My life will change a lot in the next few days. I start an affair with my family in another country, it's very close. I will temporarily stop some things, like the daily news with Telecinco. A decision I had made from the first minute because it never occured to me otherwise that I would not be with my family right now."