Solo star Alden Ehrenreich was actually casting director David Rapaport’s first choice to play Dan on "Gossip Girl", rather than Penn Badgley.

“Before Penn was involved, I desperately wanted Alden Ehrenreich to play Dan,” Rapaport told Entertainment Weekly, though producers ultimately thought Ehrenreich (at 5-foot-9) wasn’t tall enough to play a love interest for Blake Lively (who is 5-foot-10).

https://tvline.com/lists/tv-actors-almost-played-different-roles/alden-ehrenreich-gossip-girl/