ON MOTION FOR REHEARING
HILL, Chief Justice.Our opinion and judgment of May 8,1985 are withdrawn and the following is substituted. The motion for rehearing is granted.
Bill Marlin brought this declaratory judgment action to construe a clause in the will of Paul W. Drummet. The case was tried to the court which rendered a take-nothing judgment against Marlin as to the estate’s executor, Dr. Robert P. Kelley, as to the widow of Mr. Drummet, Inez Drummet, and as to third parties who were involved in the purchase of land from the Drummet Estate. The court of appeals reversed the trial court’s judgment and rendered judgment in favor of Marlin. 678 S.W.2d 582. The question before this court is whether Marlin is a conditional beneficiary under Mr. Drummet’s will. We hold that Marlin is a conditional beneficiary and affirm the judgment of the court of appeals.
Mr. Drummet had a close professional and personal friendship with Marlin for approximately twenty years, during which time Marlin served as Mr. Drummet’s real estate agent in all transactions concerning his land. Mr. Drummet relied on Marlin’s advice in all real estate matters. Marlin was present at the hospital when Mr. Drummet’s will was executed. The day before Mr. Drummet executed his will, he signed an earnest money contract for the sale of a portion of his land. This contract named Marlin as Mr. Drummet’s real estate agent. Mr. Drummet had also appointed Marlin to the Architectural Control Committee for land which Mr. Drummet owned in the area of the Houston Intercontinental Airport.
Mr. Drummet executed the will in question approximately two months before his death. The will contained five pages, four of which consisted of typewritten form pages with deletions and handwritten inser*305tions. In Item III of the will under the heading “DISPOSITION OF ESTATE”, Mr. Drummet gave and devised his entire estate “in the manner set forth on the yellow handwritten page attached hereto.” The yellow sheet contained four paragraphs. After making certain specific bequests in the first two paragraphs, Mr. Drummet left, in paragraph three, “[a]ll the rest of my property, real or personal, to my wife.” The fourth and final paragraph, referred to by the parties as the “Marlin Provision,” reads as follows:
Bill Marlin is to be the exclusive real estate agent (6% commission) for the sale by my wife of any of the real estate passing to her hereunder and he shall have a right against the sales proceeds to her to collect that commission.
After Mr. Drummet died, Dr. Kelley, the executor, commenced dealing with Marlin to act as real estate agent for the sale of a substantial portion of the real estate inherited by Mrs. Drummet. Marlin posted the real estate for sale and began seeking a buyer. About nine months after Drummet died, Dr. Kelley engaged Garland Fielder, Mrs. Drummet’s son by a prior marriage, to sell the identical real property marketed by Marlin. Approximately one year later, a substantial part of the real estate was sold for ten million dollars to World/Houston, Inc., a corporation in which Fielder was a fifty-one percent shareholder. Fielder collected a six percent commission on this sale pursuant to his commission agreement with Dr. Kelley. One year later, World/Houston, Inc. was sold to a third party for twenty-four million dollars. World/Houston, Inc.’s principal asset was the Drummet real estate. Marlin brought this suit against Dr. Kelley and Mrs. Drum-met to collect the six percent commission from the sale of the land to World/Houston, Inc.
The testator’s intent is the single most important factor in construing a will. Huffman v. Huffman, 161 Tex. 267, 270-71, 339 S.W.2d 885, 888 (1960). Since the parties agree that Drummet’s will is unambiguous, parol evidence of what the testator intended is inadmissible. Lehman v. Corpus Christi National Bank, 668 S.W.2d 687, 689 (Tex.1984). However, extrinsic evidence of surrounding circumstances is admissible to ascertain the meaning of words used in the will. Stewart v. Selder, 473 S.W.2d 3, 7 (Tex.1971); Huffman, 161 Tex. at 271, 339 S.W.2d at 888.
In this case, the testator expressed his intent in clear, unambiguous, and mandatory language: “Bill Marlin is to be the exclusive real estate agent.. .and he shall have a right against the sales proceeds to her to collect that commission.” (emphasis added). Evidence of Mr. Drummet’s professional and personal relationship with Marlin was admissible extrinsic evidence of Mr. Drummet’s surrounding circumstances.
We hold that the Marlin Provision made Marlin a conditional beneficiary and that Marlin’s interest is an equitable charge upon the land devised to Mrs. Drummet if she sells it. See Rubio v. Valdez, 603 S.W.2d 346 (Tex.Civ.App.—Eastland 1980, writ ref’d n.r.e.). Mr. Drummet would not have used such unequivocal mandatory language as “he shall have a right against the sales proceeds to her to collect that commission” had he not intended to benefit Marlin. The Marlin provision does not detract from the efficacy of Mrs. Drummet’s fee simple title, but instead creates an equitable charge upon the real estate devised to Mrs. Drummet.
Dr. Kelley and Mrs. Drummet argue that since the sale was made by Kelley as administrator it was not a sale “by my wife” within the terms of the Marlin provision. We are not persuaded by this argument. Section 37 of the Probate Code provides in part:
When a person dies, leaving a lawful will, all of his estate devised or bequeathed by such will, and all powers of appointment granted in such will, shall vest immediately in the devisees or legatees of such estate ... subject to the payment of the debts of the testator....
Tex.Prob.Code Ann. § 37 (Vernon 1980). Thus, title to the Drummet property vested *306immediately in Mrs. Drummet as devisee upon the death of Mr. Drummet, subject only to the payment of estate debts and the equitable charge imposed by the Marlin provision which was operative if the property was sold by her. White v. White, 142 Tex. 499, 503, 179 S.W.2d 503, 505 (1944). It is elementary that Dr. Kelley, as independent executor, had the right of possession and a power of sale in the estate property to pay the estate’s debts. Freeman v. Banks, 91 S.W.2d 1078, 1080 (Tex. Civ.App. — Fort Worth 1936, writ ref’d). Such right did not render this sale one not made by Mrs. Drummet within the meaning of this will and did not empower Dr. Kelley to act against the clearly expressed wishes of the testator and deprive Marlin of his right to collect the real estate commission against the sales proceeds from land inherited by Mrs. Drummet.
We affirm the judgment of the court of appeals and hold Dr. Robert P. Kelley, as Executor of the Estate of Paul W. Drum-met, and Inez Drummet liable to Bill Marlin in the amount of six percent of the total sales price paid for the land by World/Houston, Inc. to the Estate of Paul W. Drummet, deceased, plus legal interest thereon from the date of the sale.
WALLACE, J., files a dissenting opinion in which CAMPBELL, SPEARS and RAY, JJ., join.