The former couple, who split in January, hit the headlines back in October 2011 due to their 14-year age gap.
However, Tulisa has insisted that the Xtra Factor host and One Direction singer were a suitable match, brushing off suggestions that Flack is "cougar-ish and creepy".
"I've had them in my house at the same time and I've spent time apart with them as well. Harry is a very mature, charming young man, and he has enough intelligence to maintain a relationship with a slightly older woman," she told We Love Pop magazine.
"Caroline is a very sensitive, fun, young-at-heart person. The combination of the two made complete sense to me.
"People are so judgemental. She's one of the loveliest people I know. It's not cougar-ish and creepy."
Speaking of the judges' feuds on last year's X Factor, she added: "You don't need to bring it backstage. Obviously with me and Kelly, there were times when it went backstage, and we wouldn't talk, which was unfortunate. It didn't bother me though."
Flack received death threats from One Direction fans when the romance became public. She has since revealed that she had to move house due to the paparazzi interest it created.
