They call it puppy love?

Blake Lively visited new beau Ryan Reynolds on the Boston set of his flick R.I.P.D. on Sunday, which was his 35th birthday. See more pics of the new couple on set.

The 24-year-old Gossip Girl blonde (and Reynolds' love interest in The Green Lantern) was photographed peeking her head out of Reynolds' trailer as he chatted with a crewmember outside.

Before Lively left the set for the day, she left him a unique birthday present: Her maltipoo, Penny, wrapped in dozens and dozens of balloons!

The pair -- whose romance began in the wake of Lively's split from Leonardo DiCaprio in early October -- were photographed leaving Reynolds' Boston apartment on Saturday morning.

And it appears that Reynolds' birthday weekend got off to an early star in NYC on Thursday, when Lively, his pal Sandra Bullock and seven other pals joined him for a raucous meal at Carriage House at Palma Restaurant in Manhattan's West Village, followed by more drinks and entertainment at downtown club The Box.