Alex Reid told MailOnline that he is on Katie's side and is there for her if she should ever need him, despite their own relationship ending acrimoniously.
He said: "I am really sad for Katie.
"This is a terrible thing to happen and I am here for her if she needs me. I want to let bygones be bygones despite what has happened between us."
Speaking sympathetically about his former wife, the cage-fighter added: "The sad thing is, Katie has always struggled with trust issues, this is something that came up between us when we were together.
"And now it appears that she has been cheated on."
After alleging that Kieran Hayler and Jane Pountner had been having an affair for seven months, Katie - who is six months pregnant with Kieran's second child - wrote: "Kieran is a disgusting human being doing this after I've just had a baby and still doing it till I caught them
"No human being deserves this especially being 6 months pregnant
"Worse pain in the world (sic)"