Victorious Skin Question: Do I need to own Kalista to get the skin?

So last week I finally hit Gold for the first time (after 5 years, rejoice! lol), and one of the things I was most looking forward to was getting the Victorious skin for the first time. However, I noticed today in the 5.18 patch notes that Kalista is getting the skin. I do not own Kalista currently. Do I need to purchase her before the S5 rewards are given out? Or will I be given the champ for free? Or if I buy Kalista later, do I get the skin then? An official answer would be awesome. Thanks for your time!