Last week, in an interview with Vulture, she said that the rumours, which emerged in 2014, "made her sad".
She continued, "I looked at it as an exploration of trying to understand the human experience on the other side of that stardom". And I don't think of myself in that way.
Now, in a new interview on SiriusXM, she has said she suffered an additional indignity while on the Tube in London, as a man she was sitting next to began talking about her to the two women he was sitting with.
During an appearance on United States radio station SiriusXM's "Jess Cagle Show", Zellweger said she was sitting next to two women and a man "on a subway in London" when they started discussing celebrities.
"'How could she do that?"
"I tried not to think too much about the obvious which is how adored Judy is and has been through generations and how she's an icon for the ages", Zellweger said. "Of course she was extraordinary and deserved that place in history she carved out for herself among the greatest of all time, but it wasn't until we did this film that I properly came to appreciate how truly extraordinary she was by learning about the circumstances she was grappling with in the third chapter in her life". "Learning about that and watching this is what sets her apart, it's not just iconic, but heroic, really, and I was falling more deeply in love the more we learned about her as we went through". "Anyway, here's my stop'".
Zellweger said the man was "still talking about how stupid I am" when she got up just before her stop and he looked up and recognised her.
"He said, 'Oh God, you're not, you are! But you look just like yourself!' And I said, 'Yeah, it's amusing how that works, isn't it?'"
"And I'm busy! You know, I have dogs and they have to have shots and they need pills twice a day".
The 50-year-old star, who retreated from the spotlight after an appearance at the 2014 Elle Women in Hollywood Awards prompted speculation that she had had plastic surgery, recalled the "pretty painful" moment she overheard strangers negatively discussing her looks.
"The glue and the thing and the chemicals or something, I don't know, and some of it would just sneak out the crevice [on the side]", Zellweger added.
The movie, also starring Jessie Buckley, Rufus Sewell and Michael Gambon, arrives in the United Kingdom on October 4.