Should I tell my sister about my dads secret kid

Hello should I 18f tell my sister 20f about a supposed half sibling. A year ago I accidentally overheard my mother while I was eating talk to a relative of ours and keep mentioning something about how the kid was 9 when I was 8 and that the reason dad keep losing his past ​phones​ are because he gave it to them and other stuffs relating to them etc. It took me a minute to register that information and held my cousins arms and look at her like are you hearing what im hearing then I just burst into tears while there was food in my mouth and my cousin signals me to go to the restroom cuz the only barrier separating me and mom is a cabinet and so I went and sobbed there for hours. Me and my sis relationship is very barren we dont text and we fought a lot when we were kids up to teens. She goes to​ university far from home and was unaware about the details that was happening to our home (my parents are fighting and mom decided to go to my apartment at the city cuz I go to school there).

During that fight a lot of my dads secrets got exposed I lost a lot of respect for him during those months + having a secret side fam I cried for​ months straight​. Even though me and sis was enemies back in the day we are kinda neutral now and can get along. How do I tell her or do I even tell her about this my mom isn't aware that I know but my cousins on my dad side know about the secret kid and some cousins on moms side so basically mostly everyone but my sister knows and she deserves to know she is going back to univ in a few days.

Do I wait until she finishes school? Cuz my grades got affected when I was experiencing this. What do I do? Do I tell? Should I even be the one to tell? Cuz I dont want her feeling betrayed cuz we all know but her maybe im just overthinking but idk how to break this​.

Any advice is appreciated thank you very much.