David D’Alessandro, chief executive of John Hancock Financial Services Inc., resigned from his position as the Boston University Board of Trustee’s vice-chairman after submitting a resignation letter in July, reports revealed Friday.

D’Alessandro submitted a one-sentence letter of resignation to the board’s Chairman Christopher Barreca, according to The Boston Globe.

‘After careful consideration knowing the many responsibilities that are emerging in my world, I regret to inform you I will no longer serve as a Boston University Trustee,’ D’Alessandro wrote, according to the Globe.

Barreca sent out a letter to all trustees informing them that D’Alessandro had to give up his position, according to BU Trustee Esther A. H. Hopkins.

Some of the trustees said the notice came as a surprise.

‘I was surprised, although I knew he had tremendous competing responsibilities,’ said Trustee Earle Cooley. ‘I didn’t realize it had gotten to the point where he’d have to leave the board.’

Business Week reported Sunday that Manulife Financial Corporation would acquire D’Alessandro’s company in an $11 billion stock swap agreement.

Some trustees speculated that deal influenced D’Alessandro’s resignation.

‘I think he wanted to devote more time to his business,’ Hopkins said. ‘It’s obvious he has been and will be quite involved with [John Hancock] for a while.’

Other trustees said D’Alessandro left for personal reasons.

‘David D’Alessandro told me that his resignation from the Boston University Board of Trustees was for personal considerations not related to Boston University,’ Barreca said in an email.

D’Alessandro came under fire when John Hancock made a $20 million corporate sponsorship pledge for naming rights to BU’s Student Village project.

Trustees said they will miss D’Alessandro, and he was a significant part of the board.

‘I thought he was an excellent person,’ said Trustee Norman Gaut. ‘I hated to see him go. I think he’s a guy that you always want on the board, and he’s going to leave a gap.’

‘I respected him as a fellow trustee,’ said Honorary Trustee Bishop James Matthews.

Though Hopkins said all trustees received a letter about the resignation over the summer, some of them, including Gaut, said they only learned of D’Alessandro’s resignation through the media.

‘I heard about it, but that’s all I know,’ said Trustee Sidney Feltenstein. ‘I just found out about it [Thursday].’

Barreca said his resignation would not prohibit him from returning in the future.

‘We will certainly urge him to return to our board when the time is right,’ Barreca said.

Staff writers Dan Atkinson, Allison Brown, Jessica Warren and Bill Yelenak contributed to this report.