As a general rule, a court has no authority to determine what fee a litigant should pay his or her own attorney, that being a matter of contract between attorney and client. Thomas v. Anderson, 861 S.W.2d 58, 62 (Tex. App.--El Paso 1993, no writ). When the language in an attorney fee contract is plain and unambiguous, it must be enforced as written. Stern v. Wonzer, 846 S.W.2d 939, 944 (Tex. App.--Houston [1st Dist.] 1993, no writ). If an attorney fee contract was valid when made, and it was made by and between mentally competent persons, it is to be enforced without court review of the reasonableness of attorneys' fees so fixed. Parker v. Boyles, 197 S.W.2d 842, 849 (Tex. Civ. App.--Galveston 1946, writ ref'd n.r.e.). We have found in Texas state court case law the following exceptions to the general rule that attorneys' fee contracts between attorneys and clients will be enforced as written if they have been fully performed by the attorneys: (a) in cases involving fraud or breach of a fiduciary duty by the attorney, see Burrow v. Arce, 997 S.W.2d 229, 232 (Tex. 1999); Archer v. Griffith, 390 S.W.2d 735, 740 (Tex. 1964); Braselton v. Nicolas & Morris, 557 S.W.2d 187, 188 (Tex. Civ. App.--Corpus Christi 1977, no writ). (b) in cases involving minors or incompetents. See TEX. PROB. CODE ANN. 233(b) (Vernon Supp. 2000); TEX. R. CIV. P. 44; Stern, 846 S.W.2d at 947.