"Spawn my boy, you completed our family," Valderrama wrote in a heartbreaking Instagram post. "You were the alpha and my son. I saw you go from a little pup with your ears taped to the most beautiful Doberman I have ever seen... I love you so much and I am going to miss you so freaking much. Touching you and kissing you for the last time last night was so painful. I just kept thinking I hope he's feeling my touch and hearing me say he was my son and that I loved him."