Historical Rules · 3 July 2020
Rule 702.102d
Official source text from the 3 July 2020 Rules release
As a bestowed Aura spell begins resolving, if its target is illegal, it ceases to be bestowed and the effect making it an Aura spell ends. It continues resolving as a creature spell and will be put onto the battlefield under the control of the spell’s controller. This is an exception to rule 608.3a.