The papers were delivered to Shippen late Monday night just as he got out of his parked car in Santa Monica, Calif.
Shippen is at least the second person in Spears’s inner circle to be served with papers relating to the custody battle over the singer’s sons with Federline, Sean Preston, 23 months, and Jayden James, 11 months.
Spears’s close friend and frequent party pal, Alli Sims, 26, was served with a deposition subpoena at 2:30 a.m. on Sunday. Sims, who was attending a party with Spears at the time she was met by the process server, will be asked to give the court a statement about Spears’s skills as a mother.
Sims told PEOPLE earlier this month that the singer is “a wonderful mom and she is so hands-on.”
According to the current arrangement, Spears and Federline share 50-50 custody of their two sons. But last week, Federline filed for primary physical custody of the boys.
When the couple’s divorce was finalized last month, a source close to Federline told PEOPLE that the would-be-rapper, 29, was worried Spears, 25, was exposing the boys to “unnecessary risk” and that his lawyer, Mark Vincent Kaplan, “hopes to get Kevin primary custody.”
Meanwhile in a court on Tuesday, lawyers for Spears and Federline requested more time to respond to a motion filed by several media organizations, including PEOPLE magazine, to block Spears’s request to have documents in the custody battle sealed. Commissioner Scott Gordon set Sept 14 as the next hearing date.
As for Shippen, in July, a source shot down rumors that he was dating Spears. “He’s her bodyguard and manny,” a source familiar with Shippen’s employment told PEOPLE. “They’re not dating.”
• Reporting by ALEXIS CHIU