Credit: STICKMAN/; Ian Nolan/Splash News Online

Undercover lovers!

Blake Lively sure wanted to keep a low profile Monday morning. The 24-year-old Gossip Girl star wore a large hat and kept her head down as she left Ryan Reynolds' Boston apartment. 

Reynolds, 35, walked Lively out to a van that took her to the train station. Once the actress arrived, she sat alone at the station while waiting for the train to New York.

Someone who might not find Lively and Reynolds' rendezvous amusing? Scarlett Johansson

A source tells Us Weekly the 27-year-old actress is fuming that her ex-hubby has moved on with Lively. "Scarlett is pissed that he's not under her spell anymore," the source tells Us. "She realized what a great catch Ryan was." 

The source added that "things are great" for Reynolds and his new love. "They haven't had a fight yet!"