The 37-year-old cage fighter - who was married to the TV star for less than a year between February 2010 and January 2011 - says the 25-year-old builder and part-time stripper shouldn't ''trust anyone'' throughout his relationship with Katie, but he wishes the couple ''happiness'' for the future.
Speaking to Now magazine, he said: ''You're now officially on the Katie Price rollercoaster ride. I've been there and just about survived! As much as you probably don't want to hear it from me, I have some friendly advice for you.
''Grow a thick skin, keep your old friends and don't do things just to please others. Oh, and don't trust anyone at all.
''I genuinely wish you and Katie happiness. Good luck.''
Alex - who recently had a messy split from Chantelle Houghton, with whom he has a baby daughter Dolly with - also advised Kieran against buying Katie cheap-looking gifts because he got in ''quite a lot of trouble'' with her when he once purchased the millionaire a necklace which she thought was budget.
He added: ''One last tip: Don't ever buy Katie cheap necklaces. I got in quite a lot of trouble for that.
''I remember her saying, 'Just buy me Louis Vuitton in future and I'll be happy.' The kicker was that the necklace I'd bought her wasn't even cheap - actually, it was bloody expensive.''