Steve Ballmer is no longer part of the Microsoft operation.
Ballmer claimed his departure was necessary in order for him to focus on his other responsibilities, such as his ownership of the Los Angeles Clippers basketbull team.
"Given my confidence and the multitude of new commitments I am taking on now, I think it would be impractical for me to continue to serve on the board, and it is best for me to move off," he wrote to Nadella.
"The fall will be hectic between teaching a new class and the start of the NBA season, so my departure from the board is effective immediately."
Ballmer has been on the board for just six months, following his decision to resign as Microsoft CEO back in February.