Is it a felony for a convicted felon to own or to be in possession, custody or control of a firearm?

As pertinent here, section 12021 makes it a felony for any person who has been convicted of a felony under state or federal law to own or to be in possession, custody, or control of a firearm. ( 12021, subd. (a).) The ex-felon status of a person charged under section 12021 is an element of the offense which must be proved to the trier of fact. (See People v. Bouzas (1991) 53 Cal.3d 467, 479, 279 Cal.Rptr. 847, 807 P.2d 1076 [contrasting prosecutions under 12021 and those under 666 for petit theft with prior theft-related conviction].)