A lawsuit filed Friday against famed glass artist Dale Chihuly alleges another man created original paintings with the artist for 15 years but received no credit.

Michael Moi's suit, filed in King County Superior Court and the U.S. District Court for Western Washington, claims Moi participated in a “myriad of clandestine painting sessions” with Chihuly, but was never paid for his efforts, despite the artist’s promise for compensation.

“The truth behind the creation of his paintings has been intentionally hidden,” claims the lawsuit.

Chihuly hired Moi initially for building and construction work in 1999, according to the complaint, but then started receiving calls from the artist to help with his work.

The suit describes Chihuly's creative process with “a large volume of paintings” at his Boathouse, and how Moi and another man, Billy O’Neill, would help “mop out” paint as background and other extensive studio work.

Moi also claims he conceived a “Pumpkin” series in the early 2000s, and with Chihuly created “faces” for each painting.

Moi also claims he assisted in 2007 with paintings involving blow torches, and in 2012 with large plexiglass paintings, and with some of these the suit alleges Chihuly “played no role in the creative process.”

“Chihuly’s involvement was limited to signing completed works,” according to the suit.

While Chihuly granted Moi “unfettered access,” the suit claims Chihuly "sought to maintain the illusion both internally and to the public that he was the sole creator.”

The complaint, written by Seattle attorney Anne Bremner, details a close relationship between Moi and Chihuly, including sharing meals, heavy drinking, and sharing “Human Growth Hormone and Vitamin B shots provided by Dale’s doctor.”

Chihuly suffered periods of manic behavior, according to the suit. On the same day Moi filed the complaint, the Associated Press published an interview with Dale and Leslie in which the couple detail the artist's struggle with depression.

"When I'm up I'm usually working on several projects. A lot of times it's about a six-month period. When I'm down, I kind of go in hibernation," Chihuly told the AP.

Leslie Chihuly, wife of Chihuly, released a statement responding to the lawsuit. She said the claims "are completely and absolutely false. But Mr. Moi apparently thought that we would agree to pay him just to prevent him from exposing information that he considers to be embarrassing and sensational. He was wrong"

The statement goes on to say that Moi approached Chihuly in February, seeking $21 million for his silence, and threatened a lawsuit if his demand was not met.

“This disease and more recently, Dales’s advancing years, have made him more vulnerable to those who might take advantage of him.” Leslie said in a statement. “We look forward to shining a bright light on the facts and discrediting this and any other baseless claims concerning the authenticity and originality of Dales’ creative work.”

Moi's lawsuit seeks credit for the joint work and revenues derived from their sale.

Chihuly’s attorney, Harry Schneider of Perkins Coie, declined to comment about the case.