The on-again, off-again romance between Barbie and GI Joe appears to be heating up again.

Mattel and Hasbro, the world’s largest toy makers, recently held talks about a merger — the third time in the last 20 years that the two have talked about a tie-up.

A deal — which would arguably be the biggest thing to hit the toy aisle since Santa Claus — would create a toy behemoth to rival Lego, whose hugely popular toy bricks have turned it into a global juggernaut.

Hasbro approached Mattel about a potential transaction late last year, according to Bloomberg News, which published the report on Thursday.

If they consummate a deal, it would put the maker of the iconic doll under the same roof as the muscle-bound action figure. Both companies declined comment.

Last year, Mattel suffered a big blow when it lost the rights to Disney’s “Frozen” and Princess dolls to Hasbro.

Traditionally, the two have played to different strengths. Mattel, which owns Barbie and American Girl, has chased girls, while Hasbro, whose brands include Monopoly and Transformers, is better with boys.

But there are areas where the two overlap, and regulators won’t play around when it comes to reviewing a potential deal.

For example, Hasbro makes Marvel action figures while Mattel makes DC Comics action figures. The combined company could jack up prices on superhero figures.

Also, Hasbro has Fisher-Price and Mattel owns Playskool.

“The FTC will analyze competition in narrow markets,” predicted one top antitrust lawyer.

Hasbro’s shares rose 1.4 percent to $76.06, while Mattel gained 5.2 percent to $33.42.