The actor was in a relationship with the late Dark Knight star, who died aged 28 in 2008, from October 2000 to June 2001, and she has recalled her love for her former flame.
"I was very in love with him when we dated," she told fellow actor Kristin Davis on her podcast Are You A Charlotte?
"He's kind of amazing. I feel proud that I dated him. Yeah, for sure. I wish he was still alive," Graham said.
The podcast host recalled seeing the couple together at a Los Angeles coffee shop while she was working on Sex And The City.
"Yes, I dated him. And in fact, I think we might have watched (Sex and the City) together, and I think he actually really liked it ... I remember us watching it and him being like, 'I can relate to this'," she said.
"Because sometimes you try to get guys to watch it with you, and some guys loved it, but other guys would be like, 'I don't know, that's a girl show'."
Davis described the pair as a "ray of light" at the time, admitting they looked "cute" together.
"At the time you two were this ray of light in this Coffee Bean. You were giggling and touching each other. And I was just like, 'Hold it together'," she added.
"You were cute!"
Graham and Davis both admitted they wished the Sex And The City star had come over to say hello.
"But also I felt protective, like I didn't want to call attention to you because you seemed very free," David explained.
Graham also opened up on the "cool pictures" she still has of her and Ledger, and she has thought about turning them into a photo album to remember that period in their lives.
After dating Graham, Ledger had a relationship with Naomi Watts from 2002 and 2004, before moving on with Michelle Williams from 2004 to 2007, with whom he welcomed daughter Matilda in 2005.
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