Alex said she and the team had been left “absolutely devastated” by the death of researcher Charlie Mott.
“Now, before we go, we just wanted to pay tribute to one of our colleagues Charlie Mott, who sadly died at the weekend,” she explained.
“Everybody on the team is absolutely devastated. He was hugely talented and such good company. We miss him so much.”
Becoming choked up, Alex concluded: “Our thoughts are with his family and we are sending lots of love from all of us here. Good night.”
No further information about Charlie’s death was given.
In lieu of the show’s usual theme tune, The One Show credits then rolled in silence, in memory of Charlie.
A clip of Alex’s speech was then posted on The One Show’s social accounts, which led to a response from Kevin Duala, a reporter on The One Show.
Posting a picture of himself and Charlie on location, Kevin tweeted: “A lovely man, great professional always smiling on location with the world at his feet. My condolences go to all the family.”
Olympian Iwan Thomas also said: “Totally devastated, one of the nicest people I have met in this industry, always brought a smile to my face when I saw his name on the call sheet knowing I’d spend time with him.
“Talented, kind & funny, taken far too young. Will miss you Charlie boy.”
The One Show airs every weeknight from 7pm on BBC One.