Madonna's boyfriend insists he didn't cheat on her - because his mother was watching him.

Jesus Luz has blasted reports he kissed lingerie model Luciana Costa, 31, at a party in his native Brazil earlier this month, insisting it would be disrespectful as he was accompanied by his mother Christiane.

He is quoted as saying: "I danced with her, but I danced with everyone at the party. My mother was at my side at the party and never would I become intimate with a woman if my mother was nearby - even if I was interested in that person.

"I have nothing with Luciana. The next day I met her on the beach and greeted her normally."

The 22-year-old model also refused to comment on his romance with Madonna - who at 50 is 14 years older than his mother.

He added: "Even if it is true that I am with her, I would never reveal these details. I was never one to comment on my personal life and that won't change now. This is a characteristic of my personality."

Jesus was spotted "cavorting" with Luciana in his hometown of Rio de Janeiro last week (14.03.09), while Madonna was at home in New York.

An onlooker said: "Jesus was the hit of the party and all the girls went wild for him when he arrived. But Luciana was more interested than most and soon got hold of him for a dance.

"He whispered things in her ear, grabbed her hand, put his hand around her waist."