While co-hosting Live With Kelly on Friday, Kelly Ripa pressured Harrison to reveal the Bachelor with whom he didn't really get along with.
"This will just ruin my life for the next month," Harrison, 45, joked.
While Bachelor Nation would probably guess Juan Pablo Galavis from Season 18 would be Harrison's pick since the former pro soccer player didn't like to follow the rules and disappointed fans by only telling his winner Nikki Ferrell, "I like you," at the end of his journey on the show, that isn't the case.
Harrison revealed the Bachelor who rubbed him the wrong way was actually Charlie O'Connell, who starred on Season 7 of the ABC reality dating show in 2005.
"So here's the thing, after 15 years, 30-some odd people that have been through this show, there are people I get along with better than others," Harrison explained, before declaring O'Connell -- whose famous brother Jerry O'Connell has often co-hosted Live With Kelly -- as the one man he didn't "meld with" on The Bachelor.
Harrison elaborated, "Charlie and I, he was just East Coast, me, Southern kid, it was like oil and water," adding, "We just didn't get along."
Harrison, who also hosts The Bachelorette and Bachelor in Paradise, clarified, "I actually love Charlie," but timing can be everything.
"[Charlie] was, now self-admittedly, in a difficult time in his life, a little tumultuous," said Harrison. "He's come back from that, thankfully, but we just didn't really spend any time together."
O'Connell and the Who Wants To Be a Millionaire host therefore kept their distance from one another, with Harrison telling Ripa, "We just went our separate ways" after filming The Bachelor scenes.