The 26-year-old striker from Portugal received racy photos showing a Dutch fan in a variety of provocative poses.
But Ronaldo says he accidentally hit “forward” instead of “delete”, which sent the five photos to everyone in his address book, including fiancée, model, Irina Shayk.
A source said: “Cristiano’s phone has been buzzing with calls and emails from bewildered pals in the past few days.
“They have all been ringing and messaging to ask what the hell the email is about. And of course they all want to know more about the girl in the pictures.
“He’s had to explain she is just a fan who had sent him some pictures and that he made a mistake by sending them on instead of removing them.
“He is embarrassed about the whole thing and is particularly mortified at passing the email on to Irina.”
The fan sent Ronaldo flirty messages and said she wanted to be with him. One of the shots saw her wearing a t-shirt that said “too hot to handle”.
Among the people who received the photos were singer Pixie Lott and Hollywood socialite Kim Kardashian.
The former Manchester United star has been with 25-year-old Shayk since April 2010 and the pair are set to marry in 2012.