Melt 2 tablespoons butter in a large skillet over medium heat; add mushrooms and next 3 ingredients, and saute until tender. Add chicken; cook until thoroughly heated. Remove from skillet. Combine remaining 2 tablespoons butter and whipping cream in skillet; cook over low heat until butter melts. Stir in Parmesan cheese, parsley, and pepper; pour over hot cooked fettuccine, and toss with chicken mixture.