Could our Sun be the product of an ancient stellar collision?
The dynamics of the Solar System and the chemistry of the Solar System bodies don't support a hypothesis of a stellar merger later than formation of the protoplanetary disk which would have mixed-up things considerably and heavily disrupt any circumstellar disk. Thus this basically excludes any collision after the time one can start talking about a protostar, way before it even entered main sequence (as that's already the end of planetesimal formation).