It sure looks like it!

Ben Affleck's girlfriend Lindsay Shookus arrived home at their shared $20 million Brentwood mansion over the weekend with her daughter Madeline, and we couldn't help but notice that she seems to be sporting a noticeable baby bump! She even tried the age ol' "hide the belly with the purse" trick, but it didn't work on us.

We know what you're thinking... it could have been a gust of wind making her mid-section look fuller, or perhaps this striped dress was just unflattering and these pix were shot from bad angles. Well, we reviewed all the snapshots, and watched the video, and we're almost positive she's got a bun in the oven!

A source tells X17:
    "Ben and Lindsay are a lot more serious than people realize, as they've secretly been together for years. She's always told Ben she's not getting any younger, and she wants her daughter to have a sibling. They both know getting pregnant would mean tons of headlines and attention, which they're dreading, but they also feel like they shouldn't live their lives with regard to public perception."

It's not lost on us, either, that she's suddenly bringing her little girl around. If she's expecting a child with the Oscar winner, at some point they're going to have to blend their families. Rumor has it the SNL producer is in the process of permanently relocating to the West Coast to be with her man, which means their respective children will all be under one roof.

If they've really got a little one on the way, we wonder if they've already told Jen Garner? We doubt it, as she just posted a gushing Instagram tribute to the A-list actor for Father's Day. There's no way she would have done that if she knew!