The eyewitness - who was looking after the `Braveheart` star`s 10-month-old daughter Lucia when he allegedly attacked ex-girlfriend Oksana Grigorieva - had reportedly been battling cancer for some time and passed away at the weekend, RadarOnline.com reports.
The unnamed babysitter witnessed the actor`s rage first hand when he reportedly flew off the handle about Oksana leaving the couple`s daughter with the nanny to go and watch her 12-year-old son Alexander play in a basketball match.
According to a testimony by Oksana, the nanny fled to a bedroom with Lucia to escape the furore and could hear Mel ranting down the phone.
However, the woman never made a direct statement about the alleged incident to law enforcement officers, and left the star-s mansion before Mel reportedly punched his ex-girlfriend in the face as she held their baby daughter.
The unnamed employee was said to be a target of the 54-year-old actor, who branded her a "wetback" and suggested he was going to report her to immigration authorities.
Mel was allegedly recorded telling Oksana: "I will fire (name omitted) if she`s at your house. I will make it known and fire her. I`ll report her to the f***ing people that take f ***ing money from the wetbacks, ok?"