(Web Desk) - One week after Angelina Jolie and Brad Pitt's 18-year-old daughter Shiloh filed to drop "Pitt" from her last name, a source close to Pitt tells PEOPLE that the father of six is "aware and upset" about the change.
“He’s aware and upset that Shiloh dropped his last name. He’s never felt more joy than when she was born. He always wanted a daughter," says the source.
"The reminders that he’s lost his children, is of course not easy for Brad. He loves his children and misses them. It’s very sad," adds the insider.
"He’s still happy with Ines [de Ramon]," the source continues, but the distance from his children "pains him."
“He still loves all of his kids tremendously,” another source close to Pitt tells PEOPLE. “This whole process has been very hard for the whole family."
As previously confirmed to PEOPLE by someone familiar with the matter, Shiloh’s documents were filed on Monday, May 27, which also happened to be her 18th birthday.
The teenager is requesting a new legal name, hoping to go by simply "Shiloh Jolie."
Jolie, 48, and Pitt, 60, share six kids: Maddox, 22, Zahara, 19, Shiloh, Pax, 20, and twins Knox and Vivienne, 15.
“Since Angelina filed for divorce, Brad has been focused on having the best relationship possible with his kids,” the insider said.
“It's been very difficult for him. Many times, there have been long gaps where he didn't see the kids at all."