DJ/Music Producer Mark Ronson and Model Girlfriend Split

By Simon Perry and Pete Norman

09/15/2008 at 12:40 PM EDT

Mark Ronson, the DJ music producer and brother of Lindsay Lohan's gal pal Samantha Ronson, has split from his girlfriend, model Daisy Lowe, PEOPLE has confirmed.

Reps for Lowe and Ronson declined to give a reason why the pair ended their relationship after about six months.

Lowe, 19, has returned to London for a week of fashion shows. She was seen with Ronson last week at a bash to celebrate his 33rd birthday at a country home in Buckinghamshire, in the English countryside. But they parted in New York where she was working at the city's fashion week, and where Ronson has a home.

Ronson, who has produced hits for Amy Winehouse and Lily Allen, was seen out in London on Sunday night at a party to mark Winehouse's 25th birthday.

Lowe discovered four years ago her biological father was rock star (and now husband to Gwen Stefani), Gavin Rossdale, not the man named on her birth certificate. Rossdale had had a brief relationship with her mother, Pearl, in 1988.