DeGeneres and Heche dated from 1997 to 2000.
Harris, 22, pleaded guilty earlier this year to one count each of receiving child pornography and traveling with the intention to engage in illegal sexual conduct.
The daytime host's big send-off included appearances from Jennifer Aniston, Pink and Billie Eilish.
Comedians Kevin Hart and David Spade also said their goodbyes ahead of DeGeneres' final talk show episode.
The "Arrested Development" star says she expected the worst when speaking to her grandmother about her relationship with Ellen DeGeneres for the first time.
Ellen DeGeneres is stepping down less than a year after multiple claims that she presided over a toxic work environment, but the host told “Today” that’s not why she is quitting.
"That could've been a different story," the Grammy winner quipped as she touched on her unsuccessful audition in a chat with Ellen DeGeneres.
“He wanted to do something that was really different,“ she said of the "Saturday Night Live" star's new tattoos.
"I’m pulling for him, because he’s a really good guy,” the “Family Feud” host said of Jordan. "But at the same time, I got my eye on him.”
The Duchess of Sussex mewed in cat ears, devoured hot sauce on crackers like a chipmunk and held a huge crystal to her face during the segment.