The Supreme Court says in Gudelj v. Gudelj, 41 Cal. 2d 202, 212-213 [259 P.2d 656]: " 'Whether the evidence against the presumption is sufficient to overthrow it, is a question of fact.' (DeBoer v. DeBoer, 111 Cal. App. 2d 500, 504 [244 P.2d 953].) However, the presumption arising from the form of the deed may not be rebutted solely by evidence as to the source of the funds used to purchase the property. (Siberell v. Siberell, 214 Cal. 767, 773 [7 P.2d 1003]; In re Rauer's Collection Co., 87 Cal. App. 2d 248, 257 [196 P.2d 803]; and see Cash v. Cash, 110 Cal. App. 2d 534, 538 [243 P.2d 115].) Nor can the presumption be overcome by testimony of a hidden intention not disclosed to the other grantee at the time of the execution of the conveyance. (Socol v. King, supra, 36 Cal. 2d 342, 346; Watson v. Peyton, 10 Cal. 2d 156, 158 [73 P.2d 906]; Shaver v. Canfield, 21 Cal. App. 2d 734, 741 [70 P.2d 507].)