Read MoreBill Gross jumps to Janus; shares surge nearly 40%
Gross was close to being fired from bond giant Pacific Investment Management Co., due to what was termed increasingly erratic behavior, CNBC learned.
In January, Pimco's chief co-executive and expected Gross successor Mohamed El-Erian abruptly resigned, while retaining a position with the firm's parent company Allianz.
Read MoreWould have done 'things differently': El-Erian
Since then, Gross had threatened to leave Pimco and faced additional scrutiny after media reports indicated El-Erian's departure was acrimonious.
For the last year, the Securities and Exchange commission has been investigating whether the way Pimco values its bond holdings may have inflated the value of its primary exchange-traded fund, the $3.6 billion Pimco Total Return and the world's largest fund, sources told the The Wall Street Journal.
Gross had managed that fund, which had net outflows of $830 million in July, marking its 15th straight month of outflows, according to Morningstar.
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Reuters contributed to this report.