I recall going to my first opera there and saw Carmen - probably about 1955. (The Opera House was torn down in 1966). Zinka Milanov was the Carmen. After the opera my piano teacher took me backstage to see her.
I wasn't absolutely sure that it was Milanov but I googled my piano teacher and found this: The Community Concert Association presents Zinka Milanov, prima donna soprano, Metropolitan Opera Association ; assisted by Richard Wilens at the piano : [programme]. So they clearly knew each other - and now I am sure it was Milanov. My piano teacher had given up concertizing because he said it was too nerve-racking.