Sharing the moment on their Instagram page, Kensington Palace wrote: "Today The Duke of Cambridge used British Sign Language to congratulate Alex Duguid MBE, as he presented him with his honour at Buckingham Palace."
Alex has been the face of popular British TV shows Emmerdale and Coronation Street for its deaf audience for decades, as a British Sign Language (BSL) interpreter.
The Kensington Palace Instagram also paid tribute to Alex and wrote: "He is an example of how profoundly deaf people can have an impact on their community, their peers and their country. He is passionate about BSL and the need to promote and protect it."
"Alex has spent the past thirty years giving up his time raising hundreds of thousands of pounds towards community projects benefiting South Tyneside's deaf community, and teaching BSL classes through the organisation Signature, helping hundreds of people communicate with deaf people", they added further.
Royal fans were left in awe of the Prince's kind gesture and were quick to praise Prince William for using sign language to honour Alex.
A user wrote: "That's so sweet. Prince William will be an amazing King."
Another added: "How nice and thoughtful that The Duke Of Cambridge signed. Well done to Alex Duguid MBE."
A post read: "Nice gesture... congratulations, Mr Alex Duguid for your contributions to improve the lives of Deaf People."
A user remarked: "Thank you Prince William for being a true Royal family member. There was nothing you could do to save your vulnerable brother from the clutches of a DList actress trying to build an empire. You are a true future king for your country."
( With inputs from IANS )