Mal: The strength of evil is good as none when stands before four hearts as one.
Queen Leah: My daughter was raised by fairies because of your mother's curse. Her first words... her first steps... I missed it all.
Ben: I can look into your eyes, and I can tell you're not evil.
Answer: The first Descendants is unclear with this information. SPOILER WARNING. In the beginning of the song "Queen of Mean" from Descendants 3 we see pictures on Audrey's mantle with her and Ben as little kids. So we can assume that they have always had some sort of close relationship, but it still unclear as to when it was official.