Gossip Girl co-stars Penn Badgley and Blake Lively are "100% dating," a source reveals exclusively to PerezHilton.com.
And they're going public with their budding romance!
Perezcious spies spotted the pair making out at a private house party in LA on Friday night.
This is so Summer & Seth!
When co-stars date, it's a recipe for di-sas-ter.
[Image via WENN.]