The movie Triplets, starring Danny DeVito, Eddie Murphy and Arnold Schwarzenegger, is a sequel to the 1988 film Twins.
In Triplets, Julius (Schwarzenegger) and Vincent (DeVito) Benedict discover they had another brother (Murphy) who also came from the experiment.
Twins was released in 1988 and directed by Ivan Reitman, also the director of this sequel. Twins earned $112 million during its theatrical release. Today, that would be well over $350 million.