Former New York Mayor Michael Bloomberg will return as head of Bloomberg LP, the data and financial news company he founded, replacing Daniel Doctoroff who has decided to step aside, the company said on Wednesday.

Bloomberg LP, in which Bloomberg is the majority shareholder, said Doctoroff would step aside as president and chief executive at year-end.

"Bloomberg LP will not name a replacement, but rather will again be led by Mr. Bloomberg with support from the existing leadership team," the company said in a statement.

"This is a sad day for me and my company," the billionaire businessman and former mayor said in the statement. "I really wanted Dan to stay and continue in his leadership role. But I understand his decision."

Bloomberg, who stepped down as New York mayor last December, added he "never intended to come back to Bloomberg LP" after 12 years as New York's mayor.

"However, the more time I spent reacquainting myself with the company, the more exciting and interesting I found it - in large part, due to Dan's efforts.

"I have gotten very involved in the company again and that led to Dan coming to me recently to say he thought it would be best for him to turn the leadership of the company back to me," Bloomberg added.

"It was a gracious and thoughtful offer and one that I finally accepted after significant pushback and great reluctance," Bloomberg said in a statement.

Doctoroff, who became Bloomberg LP president in 2008 and CEO in July 2011, said: "I love the company and have deep respect and affection for Mike, so leaving is not an easy decision, but it is the right one for the company, for Mike and for me at this stage of my life.

"It is and has always been Mike's company and given his renewed interest and energy, it only makes sense for him to retake the helm," he added.

Bloomberg competes with Thomson Reuters.