Another volley was fired Tuesday in the $ 90 million legal battle between singer Billy Joel and powerhouse music biz attorney Allen Grubman.

Attorneys for Joel filed an affidavit in N.Y. State Supreme Court to provide further support in the singer’s lawsuit against Grubman and his partners.

Joel filed the suit last September, charging Grubman and other members of his law firm — Grubman, Indursky, Schindler & Goldstein — with fraud, malpractice, breach of contract and breach of fiduciary duty while representing Joel in the 1980s.

The suit against Grubman is directly connected to Joel’s $ 90 million fraud and breach of fiduciary duty lawsuit against former manager Frank Weber, filed in December 1989. Among other things, Joel maintains that the Grubman firm secretly acted in concert with Weber and against Joel’s best interests.

Grubman responded in October with a move to dismiss the case, categorically denying the charges and claiming that his law firm was being used as “a ‘deep pocket’ scapegoat” in the wake of Weber’s filing for bankruptcy.

The new affidavit provides numerous examples of what it says proves that Grubman, Indursky paid kickbacks to Weber’s company, Frank Management.

The affidavit says that during an FBI interview in May 1992, attorneys Grubman and Arthur Indursky said they did not remember Frank Management rendering any consulting or tax planning services to the firm.

However, the affidavit contains copies of Frank Management’s 1985 bills to Grubman and Indursky, personally, totalling $ 27,000 for “consulting services” and “financial consulting and tax planning”–as well as bills for other amounts during Grubman’s tenure as Joel’s attorney from 1981 to 1989.

Also, the affidavit gives further evidence on Weber’s allegedly having a racehorse killed to recover investment monies, citing documents showing the Grubman defendants made a $ 250,000 unsecured loan to Weber’s Silver W Stables which was used to purchase the horse “Vers La Caisse.”

Grubman and Indursky told the FBI that it was the only time they ever made a loan to a client and that they made the loan because Weber was “desperate for money” and because he was Joel’s manager. The horse died within a few months of the purchase and Silver W collected $ 890,000 in insurance payments, repaying the Grubman loan with interest.

In their response, the defendants had termed the horse-killing deal–which allegedly involves current Sony Music prez Tommy Mottola–”comic gossip.”

“Here we have details of this specific connection between Weber and Grubman,” said attorney Leonard Marks, representing Joel for Gold, Farrell & Marks. “It is hardly comic gossip.”

According to a May 21, 1992, memo Marks wrote about the FBI interview, included in the affidavit, Grubman stated that Mottola had told him about a conversation he’d had with Weber to the effect that “you can burn horses on his horse deal investment to get investment money back through insurance.”

Joel was not told of any of these dealings with Weber, according to the lawsuit.

Filed Under:

Follow @Variety on Twitter for breaking news, reviews and more