We don't know anything yet! We find out tomarrow night!

I wasn't sure if he was in a past episode or something because someone posted in a pick "How will Lucas find out about Peyton and Julian's past?" or something like that.

after lucas proposed to peyton there was a flashback scene where she met julian, then at lucas book signing after him and lindsey kissed peyton ran into him outside and he took her to a party banquet type thing. then later in the episodes it showed flashbacks of them living together and being in love. but he ended it because she loves lucas.

i knew they had a past and i knew about how they met because of the spoilers but i was not exspecting them to be in love.