'Kate & Allie' Star Jane Curtin Mourns Late Co-Star Susan Saint James

Susan Saint James' co-star on the hit show "Kate & Allie," Jane Curtin, has opened up about the death of "my friend" at the age of 80 ... talking about how much she'll miss her.

Jane told Page Six ... “We lost a decent person today. Susan St. James was a decent person who made 'Kate and Allie' a joy. She juggled a really full life from the Ed Sullivan Theater in between working on stage and being the Mom on set."

Jane added ... "Susan was my friend, and working with her brought such laughter, community and family to the stage at the Ed Sullivan Theater. I’ll miss her."

The late Emmy Award-winning actress -- who was married to NBC exec Dick Ebersol for 45 years -- died Monday after being diagnosed with pancreatic cancer, her rep previously confirmed to PEOPLE.

In their statement, her family described her as being "generous with her time and energy, which she valued more than money, and instinctively drawn to whoever needed lifting up. She taught her children to pause, be kind and look out for other people."

Jane said ... "She worked tirelessly for organizations she believed in like the Special Olympics. All the while raising children and going through the horrors of losing a child."

Susan and Dick's youngest son, Teddy, was killed in a plane crash in 2004.

Her family wrote after her death ... "Her defining act: weeks after losing her youngest son, Teddy, in the November 28, 2004 plane crash, she delivered his eulogy as a note to each of her other children and her husband, giving them words to heal."

Susan became a TV staple on "The Name of the Game" ... and her role of research assistant Peggy earned her 3 Emmy nods and a win in 1969.

She earned 3 more Emmy nods for her performance on "McMillan & Wife" alongside Rock Hudson from 1971-1976.

Then she went on to star on "Kate & Allie" opposite Jane ... resulting in 2 more Emmy nominations.

Susan was 80 ... and is survived by Dick, her 4 kids, and 7 grandchildren.