He who acts like a father, is a father — if not biologically than at least legally — the Court of Appeals said Thursday in imposing “equitable paternity” on a man who wrongly assumed he had fathered a girl and acted accordingly.

The court in Matter of Shondel J. v. Mark D., 40, upheld the trial court and the Appellate Division, 2nd Department, in ordering a man to pay child support on behalf of a child he did not father. In doing so, it recognized the legislatively endorsed concept of “equity paternity,” or paternity by estoppel (see Family Court Act �� 18 [a] and 532 [a]).