The actors were first rumored to be dating back in August, and now, the proof is in the pictures.
The couple was spotted out and about in LA together last week, grabbing juices and walking Amanda's dog Finn. They later hit a local park for a picnic with her dog in tow.
"They had a great foundation going in so it has been going very well," a source tells UsWeekly of the twosome. "They've been spending a lot of time together."
It also helps that Justin, 35, is getting along famously with Amanda's four legged friend. "He's a big dog person," the source says.
And it seems they're not trying to keep their relationship under wraps anymore. Amanda, 27, recently Instagrammed a funny photo with Justin's face imposed on a llama.