Which '90210' star did Blake Lively just post a #tbt with?

9-0-2-1-Oh em gee!  Hey there, Jason Priestley!!!!

Before Dan and New York City, Serena van der Woodsen apparently fell in love with Brandon Walsh and the 90210 ZIP code, according to Blake Lively. (How did Gossip Girl miss this?!?) The actress, who is pretty great at writing captions, said:

"#tbt to when Serena Van Der Woodsen and Brandon Walsh were a thing. (Shh don't tell @robynlively 😊😉😝)"

Blake's big sis, Robyn, actually dated the man with the perfect hair in real life. And though both married other people, it looks like everyone is on good terms.