The actress confirmed earlier this week that she is to tie the knot with boyfriend Ryan Reynolds. Westwick, who plays womaniser Chuck Bass in the US teen drama, said he was disappointed to have missed out.
Speaking at a Costume Institute gala in New York, he said: "Scarlett Johansson is probably the most beautiful because of her style. She probably does it for me.
"I'm very, very, very, very disappointed [that she is engaged]. I missed my chance. That boat has sailed."
Lost In Translation director Sofia Coppola added her congratulations on hearing the news, saying: "I hope she is very, very happy. She's super funny. I love a smart, ballsy New Yorker and that's what she is. I wish her the best."