Paul McCartney e Heather Mills Separam-se

Sir Paul McCartney and his wife of four years, former model and anti-landmine advocate Heather Mills, are separating.

"Having tried exceptionally hard to make our relationship work given the daily pressures surrounding us, it is with sadness that we have decided to go our separate ways," the couple said in a joint statement.

"Our parting is amicable and both of us still care about each other very much but have found it increasingly difficult to maintain a normal relationship with constant intrusion into our private lives, and we have actively tried to protect the privacy of our child," the statement continued.

"Separation for any couple is difficult enough, but to have to go through this so publicly, especially with a small daughter, is immensely stressful. We hope, for the sake of our baby daughter, that we will be given some space and time to get through this difficult period." The couple married in June 2002 in a $3.2 million wedding in Northern Ireland. Their daughter, Beatrice Milly, was born in October 2003.

McCartney, 63, and Mills, 37, met through her charity work, the Heather Mills Heath Trust, which provides prosthetic limbs to the needy and campaigns against landmines. Mills – who now carries the title of Heather, Lady McCartney – formed the initiative after losing the lower part of her leg in a 1993 motorcycle accident.

The U.K. press has reported recently that McCartney and Mills have been living apart in the past few weeks. Mills's rep at first denied marital woes, "She's getting a new leg fitted, and she's (in Hove), near where she's having it done. Paul's being very supportive."

NBC News reported Wednesday morning that Mills, who has said McCartney turned down her offer to sign a prenuptial agreement, could claim as much as a quarter of McCartney's estimated $1.5 billion fortune.

McCartney has three children from his 29-year marriage to the former Linda Eastman, who died of breast cancer in 1998.

They are Mary, 36, a photographer; Stella, 34, a fashion designer; and James, 28, a musician. McCartney also has a stepdaughter, Heather, 43, from Eastman's first marriage.