Alongside a picture of his 14-year-old friend, Martin shared with his 24,000 followers: “Such an unbearably sad day.
“Mylo, my 14 year old Golden Retriever has recently suffered two strokes, and on the advice of the vet he’s just been put to sleep,” he said.
“If you’ve ever lost a pet you’ll know how I feel right now.”
The TV host went on to say goodbye as he added: “Heartbroken,” which was followed by a sad emoji.
“It’s a balance between the terrible pain of losing them and the love and friendship they give you unconditionally.
“Always hold onto the latter and know you gave them the best life possible.”
Martin has presented the hit property programme since 2003.
Elsewhere, the housing expert recently chatted to some of his viewers during his weekly Q&A on Twitter, answering any of their burning questions about the show.