Tom Cruise's mother, Mary Lee South -- who in recent years had battled health issues -- died in her sleep.

The former special education teacher was the driving force behind Tom's pursuit of acting. He frequently credited her for inspiring him.

She died last week and a service was already held ... which Tom and his 3 sisters attended.

We last saw her back in 2013 when we tried getting her to spill some Christmas secrets.

LAST TIME WE SAW HER
TMZ.com

People first reported the death.

Mary Lee was 80.