The formerly married couple - who have two kids together - had a famously painful split, which was played out in the public eye.
Until recently they did not speak to each other...
But all that has changed with the passing of time, and now Katie, 37, has revealed she recently attended Peter's gig in Brighton!
Posting a video from the crowd onto her Instagram account, the Loose Women star wrote: "Great concert this song brings back memories."
Peter can be seen singing 'Insania', the song he penned while in the I'm A Celebrity jungle, where he and Katie fell in love.
Awwww, we love it when people make-up!
If that wasn't sweet enough, the footage pans around to show son Junior and Katie's new husband Kieran Hayler in the audience enjoying the music. In fact, Pete's two children with Katie - Junior, 10, and Princess, 8 - both joined dad on the stage later on.
One fan responded with the message: "So glad you and Pete are friends again."
Another wrote: "Thinks it's lovely that you all go and watch him. The past is the past and can't be changed."
And one follower added: "So pleased you two have finally sorted your differences out!"
Katie and Peter were married from 2005 to 2009. She is now wed to Kieran, while Peter has new wife Emily MacDonagh.
Just last month, the pair shocked fans when they broke their long-standing social media silence with a sweet exchange on Twitter.
Peter sent a smiley face to Katie, who later responded with two laughing crying emojis and a winking face.
The tweets came after Katie revealed the pair were on good terms and also praised Pete's wife Emily in a recent interview.
Peter also confirmed on Lorraine that things are "nice and civilised" between himself and Katie.
"We see each other when we see each other with the kids" he said. "It's all nice and very civilised. We get on really well, which is excellent, so that just adds to the peace and serenity. And the kids are really happy and it's really nice."
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