Anthony Julius will represent Mills McCartney, the law firm Mishcon De Reya said Tuesday. Julius helped Diana win a reported $28 million settlement.
McCartney, who does not have a prenuptial agreement to protect his estimated $1.5 billion fortune, had already hired Fiona Shackleton, who represented Prince Charles 10 years ago.
"It's all getting Muccy!" the Sun said, playing off McCartney's nickname in Britain -- Macca. The Daily Express summed it up by saying, "All you need is hate."
"It is a private matter," Mills McCartney spokesman Phil Hall said Wednesday. "Comparisons to Diana and Charles are irrelevant."
McCartney's spokesman, Stuart Bell, also declined comment.
Though the 64-year-old entertainer and 38-year-old anti-landmine campaigner had promised an amicable split, the facade cracked Monday when Mills McCartney found the locks changed at McCartney's London home.
A security guard at the home called police when one of Mills McCartney's guards climbed a wall to let her enter. Police spoke to her and then left -- but not before the waiting paparazzi snapped photos as she stood in the street beside a uniformed officer.
Security guards drove the couple's 2-year-old daughter Beatrice around the block while the situation with the police was sorted out.
Hall said McCartney had frozen the couple's joint bank account and sent Mills McCartney a letter complaining about three bottles of cleaning liquid that were taken from his home to her office.
The couple married in June 2002, four years after McCartney's first wife, Linda, died of breast cancer.
Critics charge that Mills McCartney has long emulated the late Diana, in part by choosing charity work to fight against land mines -- as the princess had done. The sniping increased with her choice of attorney.
The Sun's Showbiz editor, Victoria Newton, took a hard line in a column headlined, "Lady Mucca's war of lies," and suggested Mills McCartney would never have the public appeal that won Diana the nickname, "Queen of Hearts."
"She may aspire to be the Queen of Hearts -- but all she will ever be is the Queen of Tarts," Newton wrote.