It's never easy to lose a loved one, particularly over the Christmas period.
Taking to her Instagram, Stacey revealed the emotional news that her beloved pooch passed away in her arms on Boxing Day morning.
Sharing a selection of her favourite photos with Theo, the Loose Women presenter wrote: "The best friend we could have ever wished for. Our hearts are broken. Yesterday at home in our arms we had to say goodnight to our Theo. 11 wonderful years.
"We were so lucky to love you Fifi and we will never stop."
Stacey continued: "My lap has never felt so empty. I miss you so much already. My little girl. But oh my goodness the memories and the love you brought into our lives!
"For protecting me and the boys when we needed it most. For loving us no matter what and for holding on for so long and waiting to meet your little sister Rose.
"Rex has had the best friend in you that he could ever have wished for and the boys have had the best protector in the whole wide world. Even though Rex is only little I know him, Zachary and Leighton will never ever forget you."
Fans were quick to send their love to Stacey, who also shared photos of Theo, the pomeranian-chihuahua mix, to her Instagram stories.
"I’m so sorry for your loss," wrote one fan in the comments, adding lots of kisses to Stacey.
"Sending lots of love," added another.
"Sleep peacefully, Theo," said a third, while another said: "So sorry to hear about beautiful Theo."
Stacey's fellow Loose Women panellists were also quick to express their sympathy.
"Oh Stacey….I’m so, so sorry," said panellist and This Morning host Ruth Langsford. "Heartbroken doesn’t even come close. "What a wonderful life she had with you all though….hold on tight to those memories. Sending you all love and a huge hug."
"Oh Stacey I’m so sorry darling," added Nadia Sawalha.
Stacey has previously spoken out about how much Theo means to her.
Naming the pooch after her favourite footballer at the time, Theo Walcott, Stacey described Theo as her "second child," as she purchased the pooch shortly before giving birth to her son, Leighton.
We're sending all our love, Stacey!