Appeal from the Circuit Court of Cook County. No. 01 L 50811 The Honorable Bernetta D. Bush, Judge Presiding.
 The opinion of the court was delivered by: Justice Garcia
 The defendant, the Retirement Board of the Fireman's Annuity and Benefit Fund of Chicago (Board), appeals from a circuit court order reversing the Board's decision denying plaintiff, Idella Bertucci, a widow's duty-related annuity benefit pursuant to section 6-140 (40 ILCS 5/6-140 (West 2000)) of the Illinois Pension Code (Pension Code) (40 ILCS 5/1-101 et seq. (West 2000)). We affirm.
 The plaintiff's husband, James J. Bertucci, became a fire fighter with the City of Chicago (City) in February 1969. In September 1991, James was injured while on duty. James's injury stemmed from a fall from a fire-truck ladder. As a result of his fall, James suffered a spinal-compression fracture of the L-1 lumbar vertebra. In August 1992, James filed an application for disability benefits with the Board. In October 1992, the Board granted James duty-related disability benefits. 40 ILCS 5/6-151 (West 1992).
 In December 1994, January 1997, and March 1998, James was examined by a physician for the Board, Dr. George S. Motto. James's reexaminations were statutorily prescribed; "however[,] such annual examination may be waived by the Board if the appointed physician certifies in writing to the Board that the disability of the fireman is of such a nature as to render him permanently disabled and unable ever to return to service." 40 ILCS 5/6-153 (West 1992). In his March 1998 written report to the Board, Dr. Motto determined there was "no way [James] could improve." Also in the March 1998 report Dr. Motto found James "permanently disabled due to prior injury," and opined that James would "never return to work." James, in fact, did not return to work as a fire fighter and continued to receive duty-related disability benefits until his death from metastatic*fn1 lung cancer in April 2001.
 In May 2001, the plaintiff, relying on section 6-140 of the Pension Code (40 ILCS 5/6-140 (West 2000)), filed an application for a widow's duty-related annuity benefit with the Board.
 In June 2001, the Board held a hearing on the plaintiff's application. The plaintiff testified she and James were married in 1964 and remained married until his death. Dr. Motto testified that in March 1998, "[James] was permanently disabled due to [James's] lower-back pain," which stemmed from a spinal-compression fracture due to James's 1992 fall from the fire-truck ladder. Dr. Motto also testified that cancer was the cause of James's death and that the cancer was not caused by an act of duty. The Board denied the plaintiff's application for a widow's duty-related annuity benefit under section 6-140 of the Pension Code (40 ILCS 5/6-140 (West 2000)). However, the Board granted the plaintiff a widow's non-duty-related annuity benefit under section 6-141.1 of the Pension Code (40 ILCS 5/6-141.1 (West 2000)) based on its finding that James did not die in the performance of an act of duty because he died from lung cancer. The Board also granted James's disabled adult son a child's annuity (40 ILCS 5/6-147, 6-148 (West 2000)); the child's annuity award is not at issue.
 In July 2001, the plaintiff filed a complaint for administrative review of the Board's decision with the Cook County circuit court. In September 2002, the circuit court heard argument and reversed the Board's decision based on section 6-140 of the Pension Code (40 ILCS 5/6-140 (West 2000)) and this court's holding in Tonkovic v. Retirement Board of the Firemen's Annuity & Benefit Fund, 282 Ill. App. 3d 876, 668 N.E.2d 1126 (1996). This appeal followed.
 I. Standard of Review
 We review the decision of an administrative agency, not that of the circuit court. Swoope v. Retirement Board of the Policemen's Annuity & Benefit Fund, 323 Ill. App. 3d 526, 529, 752 N.E.2d 505 (2001). Generally, "[a]n administrative agency's findings of fact are deemed prima facie true and correct." Swoope, 323 Ill. App. 3d at 528-29, citing City of Belvidere v. Illinois State Labor Relations Board, 181 Ill. 2d 191, 204, 692 N.E.2d 295 (1998); 735 ILCS 5/3-110 (West 2000). Further, if the record contains any evidence to support the agency's decision it should be affirmed. Abrahamson v. Illinois Department of Professional Regulation, 153 Ill. 2d 76, 88-89, 606 N.E.2d 1111 (1992). However, an administrative agency's conclusions of law are afforded less deference and are reviewed de novo. Swoope, 323 Ill. App. 3d at 529, citing City of Belvidere, 181 Ill. 2d at 205.
 The circuit court characterized the issue before it as one of law, "[w]hether or not the Board appropriately interpreted the section 40 ILCS 5/6-140 and the Tonkovic case, which *** gave an analysis of that particular provision." The circuit court applied a de novo standard of review. The Board, while challenging the circuit court's ruling, does not contest that the issue turns on the "interpretation of its own statute." Nonetheless, the Board contends that the appropriate standard of review is the clearly erroneous standard because it is entitled to deference based on its experience and expertise. The facts, however, are not in dispute. Thus, the resolution of this case depends, not upon evidence heard by the Board or even the application of those facts to the law (a mixed question of fact and law to which a clearly erroneous standard should apply), but upon the purely legal question of the proper interpretation of the statutory provisions governing annuity benefits for the widows of fire fighters. See City of Belvidere, 181 Ill. 2d at 205; 40 ILCS 5/6-140, 6-141.1 (West 2000). This is a question of law and therefore, our review of the Board's decision is de novo. See Shields v. Judges' Retirement System, 204 Ill. 2d 488, 492, 791 N.E.2d 516 (2003).
 The Board contends that the Tonkovic decision, which the plaintiff maintains controls the outcome here and upon which the circuit court based its reversal of the Board's denial of duty-related benefits, is at odds with its interpretation of the controlling statute and should not be followed. Instead, the Board asserts we should follow the Swoope decision. In its reply brief, the Board asserts that the statute at issue in Swoope (40 ILCS 5/5-144 (West 1998)) and the statute at issue here ...