Brian Austin Green and his wife Megan Fox split earlier this year, and he is not happy with how it’s playing out. The 90210 star recently vented his frustration on IG, clearly mocking a shot that Fox posted with new love Machine Gun Kelly with the same caption: “My heart is yours.” His photo included their three boys.

A source tells People that Green is hurt that Fox has moved on so publicly: “Brian is annoyed that she is so focused on her relationship with Machine Gun Kelly. He doesn't understand the need to post social media pictures with silly captions to proclaim her love for him. They aren't even divorced yet. It definitely annoys Brian. And it stings a bit too that Megan moved on so quickly. Megan was always very private, so Brian just doesn't get what changed.”

Fox and Kelly were first linked in May, and Fox and Green announced their split soon-after, but first, he defended her against the rumors. He said: “Everybody is judgmental right now that she’s out of the country working and she’s not around. We travel and we work. It’s no different than before, we’re just no longer together. This is what we’ve been doing for 15 years. When one person is traveling and working the other person will step in and take care of things at home and the kids and this situation is no different. It’s not for lack of caring. Megan loves her kids, would do anything for them, and has and will continue to.”

Green has been caring for the sons he shares with Fox, Noah Shannon, 7, Bodhi Ransom, 6, and Journey River, 3, as she wraps up filming her latest film with Kelly. They married in 2010 after meeting in 2004.