Brittany Cartwright Denies That Her and Jax Taylor's Breakup Is a Publicity Stunt

Jax Taylor and Brittany Cartwright are putting on a united front ahead of their son Cruz's latest milestone.

Despite The Valley stars' recent separation, the estranged couple are reuniting this weekend to throw an adorable "Three Rex"-themed birthday party for Cruz, who turns 3 on April 12.

"Cruz loves dinosaurs," Brittany exclusively told E! News, "so we naturally had to choose this theme."

The celebration, which is being planned by Picnic + Petal with decorations by Glitz and Gather, will take place at an L.A.-area Skyzone trampoline park. Fellow Bravo stars expected to be…