Real Madrid frontman Cristiano Ronaldo was reportedly left "fuming" after learning that his sister had had sex in his bed.

The allegation was made by Claudio Coelho, who dated Ronaldo's sister Katia Aveiro for six months in 2013, as he appeared on a Portuguese reality TV show.

Coelho claims that he slept with Aveiro in Ronaldo's bed at the footballer's home in northern Portugal and he became enraged once he discovered what had happened.

"It is normal for Cristiano not to like other people occupying his personal space," Coelho said, according to The Sun. "I understand him fully. But the problem is that his sister has little judgement, despite being almost 40 years old.

"Katia and I were visiting the Geres area, and spent the weekend at Ronaldo's house. That was where we slept together for the first time."

Aveiro has forged a career as a singer in Portugal under the pseudonym 'Ronalda'.