From his Instagram post:

My experience in college has by far. more than anything else in my life, shaped me into the young man I am today. I have met friends that I will cherish forever. Villanova University is a very special place, and it holds an even more special place in my heart. And to my teamma- no to my brothers I will love you guys forever. Coach Wright has helped me mature as a man along with some of the best coaches in the country Kyle Neptune, Ashley Howard, George Halcovage, and Mike Nardi. I will forever appreciate everything done for me. To the Nova Nation, thank you for the support and love I have received as a member of the family and community, that is something that I will cherish forever and I know Villanova is a place I can always call home. And last, but probably the most important to me, is my mother away from home, Arleshia Davidson. We share a love and bond that will never be broken.
In saying this, I would like to announce that I will forgo my final three years of college eligibility and remain in the NBA Draft!
THANK YOU FOR EVERYTHING NOVA NATION!!!

NBADraft.net currently has Spellman going 26th overall to the Sixers:

Of course, they could also take Donte DiVincenzo or Jalen Brunson to go along with Mikal Bridges in couping two of the four first round draft picks from Villanova.