Ben Affleck and Jennifer Garner seemed like ''strangers'' on his birthday.

The estranged couple reunited on Saturday (15.08.15) for the 'Batman v Superman' star's 43rd birthday, which they spent with their three children at the Wizarding World of Harry Potter attraction in Orlando, Florida, but onlookers say the scene wasn't particularly friendly.

According to one eyewitness ''neither of them looked too happy''.

The couple enjoyed the day with their children, Violet, nine, Seraphina, six, and Samuel, three, as well as Ben's mother Christine.

The eyewitness added to PEOPLE.com: ''They didn't even look at each other. They were talking to the kids, but they didn't talk or even look in each other's direction. They seemed like strangers - awkward strangers.''

Ben has recently battled claims that he cheated on Jennifer with their former nanny, Christine Ouzounian.

The Oscar winner denied any ''all allegations of a romantic relationship'' and said the speculation was ''baseless and untrue''.

Ben and Jennifer have been insistent on putting on a united front for their children.

A source previously said: ''They feel like they have to be mature adults for their children's sake and that they will figure out the healthiest way to co-parent. They want the kids' lives to stay the same and to not have to change just because they aren't going to be married anymore.''