Gross is joining Janus Capital Group, effective Sept. 29, the company said. The 70-year-old investor will manage the recently launched Janus Global Unconstrained Bond Fund and will join the Janus team focused on global asset allocation effective Oct. 6, 2014, the company said.
Read More Bill Gross jumps to Janus; shares surge nearly 40%
Gross was about to be fired from Pimco due to what was termed increasingly erratic behavior, CNBC has learned. To Bogle, though, Gross might have just had enough with what had lately seemed to be perpetual problems and ongoing drama at the Newport Beach, California-based firm.
"Maybe all the politics that came into be involved in the management of Pimco, the SEC challenging the pricing of some of his bonds [and] all those little fits probably just drove him up the wall and he said, 'Who needs this?'" Bogle said on "Squawk on the Street." "Now I can't read his mind, but if he wasn't thinking that way, I'd be a little surprised."
Bogle, who himself is considered to be a mutual fund pioneer, had high praise for the "Bond King."
"He's a true giant in the industry. He's a true legend. He's earned all that," Bogle said. "There aren't so many people in my field that actually measure up to that test. Bill would be right at the top of that list."
—CNBC's Jeff Cox contributed to this report.