BOSTON (CBS/AP) — William Gross was sworn in Monday as Boston’s first black police commissioner.

Gross took the oath at the Morning Star Baptist Church in Mattapan, where his mother Deanna has been a member for 35 years. She placed the commissioner’s badge on her son after he was sworn in. Gross later gave the badge to her, along with a bouquet of flowers.

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William Gross’s mother put the commissioner’s badge on her son as he was sworn in as the city’s first black police commissioner, August 6, 2018. (WBZ-TV)

Mayor Marty Walsh called it a “historic occasion,” saying Gross is not only Boston’s first black police commissioner, but “America’s next great police commissioner.”

Gross said he’s humbled by the promotion and thanked the seniors in the room who paved the way for him to get there. He takes over from William Evans, who announced last month that he was retiring after nearly 40 years in the department. Evans took a job as police chief at Boston College.

Gross thanked Evans and noted how they worked together the last four-and-a-half years “bringing the whole city together.” Gross said they knew “people were looking at us,” two men from South Boston and Dorchester, because of their different skin color and Boston’s turbulent racial history.

He then shared their favorite joke.  “I’m trying to get him to eat, he’s trying to get me to run,” Gross said, in a nod to Evans, who has finished several marathons. Then, “in his cool DJ voice,” Gross said imitating his predecessor, “he says and ‘When we go down the street, we look like the number 10.”

Boston Police Commissioner William Gross sworn in, August 6, 2018. (WBZ-TV)

He also praised his mother Deanna. “She brought forth the love to entire communities. Thank you mom,” Gross said.

Gross joined the force in 1985 and worked his way up from a patrol officer to its second-in-command in 2014. He has long been one of the public faces of the department and is well-known in the community.

Gross also paid tribute to recently fallen officers Ronald Tarentino in Auburn, Sean Gannon in Yarmouth and Michael Chesna in Weymouth, saying their spirit will never be taken away by their killers because “we will not let them.”

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WATCH: Commissioner Gross’ Speech

Hours after the ceremony, Gross set a unifying tone as he strolled from Brighton to Roxbury with Mayor Walsh. Commissioner Gross shook hands and gave out hugs.

It’s a historic moment that Wendy Johnson wanted to share with her two young sons at one of the stops in Hyde Park. “It just means progress,” Johnson said. “This is a stepping stone for my boys because we use this as an example. We use this as all the things they can accomplish.”

Now that he’s at the top Gross hopes to give back by encouraging more people of color to get involved and join the force. “No matter where you are, you should be welcome,” Gross said. “You will be welcome to put on a blue uniform.”

WBZ-TV’s Tiffany Chan reports

It’s a moment of inspiration for 9-year old Brandon Garden who waited anxiously to meet the man himself in Hyde Park.

“We kids are going to be like the future commissioners,” Brandon said. “We’re going to rise up and I hope that all the kids out there, any type, that no one clips our wings and that we fly high.”

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(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)