Sean Penn described his ex-wife Madonna ''so hot'' when he saw her in concert recently.

The 'Milk' actor - who had a stormy four-year marriage to the singer from 1985 to 1989 - attended her show at Los Angeles' Staples Center earlier this month and onlookers said the pair still had incredible chemistry.

A source said: ''Their chemistry was off the charts. Madonna seemed to be performing entirely for Sean. And he was saying things like 'amazing' and 'she's so hot!' ''

Despite the obvious bond between the two, insiders insist Sean and Madonna - who is currently dating dancer Brahim Zaibat - would never reconcile as the singer prefers to be in relationships with people she ''can control''.

A source told Us Weekly magazine: ''They've remained close friends. But they are fire and fire together romantically. She can only be with someone she can control.

''Madonna's friends wish she'd get back with Sean. He will always be the love of her life.''

Shortly after the gig, it was claimed Madonna, 54, was deliberately teasing 52-year-old Sean with her performance.

The witness said: ''At one point she stared Sean dead in the face, smiled, unzipped her pants and mooned the crowd, but it was really like she was mooning Sean! He laughed and clutched his chest like he was going to pass out. She was wearing a black lacey thong, and her butt looked perfect! So smooth and tight ... like a 20 year old's!''