Rob Lowe is speaking out about his decision to quit NBC's

The West Wing next season. Basically, the former Brat Packer says he grew tired of playing third fiddle on the Emmy-winning drama. "As much as it hurts to admit it, it has been increasingly clear, for quite a while, that there was no longer a place for Sam Seaborn on The West Wing," he said in a statement. "However, Warner Bros. has allowed me an opportunity to leave the show as I arrived... grateful for it, happy to have been on it and proud of it." Meanwhile, co-star Martin Sheen tells TV Guide Online: "Frankly, we're all heartbroken and a bit concerned because we've become so close. I've known [Rob] since he was a boy. I think it's the best work he's ever done, and he's elevated his image to the public to a great level. I just have to let him go and wish him the best." Lowe will be written out in next season's 16th episode, which will likely air in March.