It was the second accusation of underage sex made public in the past two weeks against Clash. The first accuser, an unidentified 23-year-old man, later recanted his claim.
Herman said Singleton chose to speak out now in order to "spare the lives of others like him and to begin his own healing process."
"According to our lawsuit, Kevin Clash preyed on vulnerable teenage boys, like Cecil Singleton, to satisfy his depraved sexual interests," Herman said.
Singleton, now in his 30s, claimed he met Clash in a gay chat
line in the early 1990s and had his first sexual encounter with him when he was 15 years old, according to details of the complaint posted on Herman's website
During those alleged phone interactions, Clash allegedly "persuaded, induced, coerced or enticed" the teenager to meet him for sexual encounters, gaining his trust by taking him to fancy dinners and giving him money.
Clash did not acknowledge the new allegation, but said he was resigning due to "personal matters."