The mother of five shared a quote which read: "Love is accepting people for who they are. No matter what."
She added the caption "hubby" to make sure we knew who the note was aimed at.
Katie, 38, and Kieran, 29, are currently in the Caribbean enjoying a romantic holiday, which Katie has called a "belated honeymoon". They tied the knot in the Bahamas in January 2013 and renewed their vows later that year.
The vacation came after Katie announced she'd be taking a break from Loose Women to focus on her marriage and kids, after promoting new autobiography Reborn brought back "old wounds" about Kieran's affair with her close friend Jane Pountney.
Katie was pregnant with Kieran's second child, Bunny, when she learned he'd been sleeping with Jane behind her back. The affair started while Katie was expecting their first child, Jett.
She documented the betrayal and aftermath in Reborn.
But Katie explained on Loose Women: "We had therapy [after I found out about the affair] and I thought I was OK. But the past two weeks I've been on my book tour and it's opened up some wounds. It's been awful. I thought I'd dealt with it. But when I look back, I had just had babies and was concentrating on them and I was numb when it all happened.
"I want to help Kieran through this as well. It's been tough on us both. It's been turbulent."