BT Group chief executive Gavin Patterson is leaving after five years at the helm of the former British phone monopoly, following a strategy reset that failed to win over investors.
Analysts at Bernstein said it was no secret that Patterson was under enormous pressure, but added that the timing of the announcement was "highly puzzling and worrying".
Chairman Jan du Plessis said the board was fully supportive of Patterson's strategy but that a new leader was needed.
During his time at the helm, Patterson has overseen a number of changes in the business, not least its entrance into the TV market.
He said: "It's been an honour to lead BT since 2013, and serve as a member of the board for the last 10 years".
The company has been dealing with the aftermath of an accounting scandal at its Italian division, which resulted in a £530 million write-down and a major fall in its share price a year ago.
Joppa group lands winning $50K Powerball ticket
The father of two made a decision to take the $183 million cash payout and remain in his New Jersey hometown. A New Jersey man came forward as the victor of the $315.3 million Powerball jackpot.
French Open 2018: Rafael Nadal wins 11th title
And he increased the tempo further, consigning Thiem to defeat in his first major final when the Austrian sent a return long. However, in Open Era, he is the first player ever (man or woman) to complete La Undécima in a single Grand Slam event.
Despite this, Mr Patterson managed to head off a threat to split BT's Openreach broadband division into a separate company. After Friday's announcement, the shares rose by 2.5 percent.
Last month, the company announced an ambitious restructuring. This was offset partly by hiring 6,000 new employees - including 3,500 engineers - to help implement BT's 3.7 billion pound investment in its 5G mobile services.
But the admission that fraud had left a 530-million pound black hole in its Italian business, combined with sharp slowdown in demand from public sector and corporate customers, forced the 50-year-old executive to cut profit targets in 2017.
Under increasing pressure, Patterson announced a radical plan to cut job and save 1.5 billion pounds a year by 2020/21 last month.
When you devise a strategy which has the "full support" of the board then you expect that you will be around to execute it. Gavin Patterson's departure is unusual in the sense that the board liked his plan, but didn't think he was the person to carry it out. The first and most important is the share price.