And now a source confirms to People Magazine that the former Beverly Hills, 90210 star is indeed not happy over her moves.
'Brian is annoyed that she is so focused on her relationship with Machine Gun Kelly,' the source stated. '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.'
The 47-year-old is also shocked by how she fell for 30-year-old Machine Gun Kelly so soon after they split.
Megan, 34, and Brian reportedly separated late last year. 'It stings a bit too that Megan moved on so quickly,' the source added.
The insider then said that Green doesn't recognize Fox these days as she is like a different person with her public displays of affection on social media.
'Megan was always very private, so Brian just doesn't get what changed,' the source said.
Fox has been anything but covert with MGK as she even cuddled him a week ago in a photo shared to Instagram and called him 'an achingly Beautiful Boy.' She then added, 'My heart is yours.'
Green was quick to strike back as he then shared a photo of his four sons and mimicked her caption with, 'Achingly beautiful boys..... my heart is yours.'
Megan has not make an Instagram post since.
Fans were quick to defend Fox after Green made his copy cat post, but he laughed it off with a hysterical laughing face emoji on Wednesday.
Brian and Megan share three children together Bodhi, six, Journey, four, and Noah, seven, while he also has another son Kassius, 18, - who features in his post - from his previous relationship with actress Vanessa Marcil.
The pair filed for divorce after 11 years of marriage citing 'irreconcilable differences' in May this year.
Brian had stressed in his podcast back in May that he didn't want Megan and Kelly to be seen as 'villains' or that he was a 'victim.'
He also played it cooler when he said in July he will 'just keep my head down and do what I do and focus on the kids. I know she’s going to do the same thing.'
But Green has had his share of public dates too.
He was first linked to former reality TV star Courtney Stodden then moved on with influencer and model Tina Louise.
On Tuesday the actor was seen with Jane Seymour's daughter Jennifer Flynn as they hugged on the street.
The two are business partners.
Jennifer and Brian's company, called InteliQore, helps people combat cyber-crimes in real-time. They launched it after both experienced online bullying and harassment in their respective fields.
The duo also have an upcoming cybersecurity product, TRIPP, which Flynn's mother Jane is also a partner in.
