Citymapper President Omid Ashtari is leaving the company to join market research start-up StreetBees, according to people familiar with the situation.
Ashtari, also Citymapper's head of business, has been with the urban navigation start-up for over six years, making him one of the longest serving employees.
Citymapper did not immediately respond to CNBC requests for comment.
His departure comes after what was characterized as a falling out between himself and Azmat Yusuf, Citymapper's CEO and founder, according to two former Citymapper employees who asked to remain anonymous given the nature of the discussions.
"Omid had been at Citymapper since the early days and always used to be Az's right-hand man, but they had a big falling out at some point in the last couple of years, so when I was there they would barely talk to each other except to make dismissive comments," one of them said.
The other said: "Things were strained between them when I was there."
Ashtari denied there had been any falling out. "There has been no falling out with Azmat and my departure is very much amicable," he told CNBC. "After more than six years with Citymapper I'm looking for a new challenge and am excited about the opportunity at Streetbees. I will still formally stay involved as an advisor with Citymapper."
Ashtari has been an investor and non-executive director at StreetBees since September 2016, according to his LinkedIn profile.
He is understood to have handed in his notice at Citymapper around April and is expected to leave in the next month or two.
Before joining Citymapper, Ashtari spent seven years at Google, and two and a half years at Foursquare, where he was the managing director of Europe.
Citymapper's app provides transportation options for 42 cities worldwide including London, New York, Moscow, Boston, Seattle, Paris, Berlin, Hong Kong and Melbourne. The app consistently appears in the top 10 free navigation apps in the App Store and the Google Play store.
Citymapper has not had an obvious revenue stream for much of its life. However, it has experimented with several products over the last few years including a "smart" bus service and a "Citymapper Pass" that can be used to access transport across London.
The bus service — known as Smartbus, then SmartRide, then Ride — was launched in 2017 and terminated in 2019, while the Citymapper Pass lives on.
Citymapper's most recent company accounts show that it has racked up losses in excess of £20 million.
The company is on the hunt for a buyer, according to a Sky News report from January. Apple, Google, and Uber have all been linked to a Citymapper acquisition at one stage or another but a sale has never gone through.
The company raised a $10 million series A round led by Balderton Capital in 2014 and a $40 million series B round led by Index Ventures and Balderton in 2016.
Earlier this week, Ashtari told CNBC that Citymapper had raised another round of capital from external investors.
Citymapper and StreetBees did not immediately respond to CNBC's request for comment.