“It hadn’t gotten lost, but there were no files on where it was sold,” said Ginny Neel, Hartley’s wife, who did not know the identities of the boys in the painting. Ms. Goldstein died in 2006; her partner, Sandra Powers, declined to answer questions about the painting. In 2011, the painting passed quietly to the private Tia Collection in New Mexico, where it remained until an exhibition in Tucson, Ariz., in 2016.
It was just one of the loose ends in Alice Neel’s long career. “There are paintings she gave away in the ’30s and ’40s that we don’t even know exist until they come up for auction,” Ginny Neel said.
Mr. Tobias continued to look for the painting. Jeff and Gina Neal raised their family. Ms. Neel died in 1984; Toby Neal died in 2010. Finally, a photograph of the painting, truncated, surfaced in the catalog for a 2017 exhibition at the David Zwirner gallery in New York, but the painting was not part of the show.
When Mr. Tobias showed the catalog to Mr. Neal, “I was ecstatic,” Mr. Neal said. “Because that was something that I was looking for for the longest time, and it would be an honor for me to be able to represent that picture for me and my brother. I’m still here. Alice is gone, and Toby is gone.”
The week before the Metropolitan Museum show opened, Ginny and Hartley Neel, Jeff and Gina Neal, their son Desmond and Mr. Tobias all had a private viewing of the painting that had eluded them for so long.
Randy Griffey, one of the curators, said it was “special” to be able to connect a name and person with one of Ms. Neel’s anonymous portraits.
Mr. Tobias gleefully moved between the Neel and Neal families, telling stories from a half century ago, of a different world. He saw the painting as an artifact of two friendships — with Ms. Neel and with the Neal brothers — and of a city that once fostered such connections. Hartley Neel called it a record of trust between his mother and the people she painted, the absolute openness of the two boys to a wholly new experience.