"How one man can change so dramatically and quickly in one situation in life!!" wrote Mark, who had the reputation as a ladies' man in reality show TOWIE. "#partyboy to the opposite!! Not ashamed to say it #number1 #MK."
The 27-year-old's sweet message prompted a host of positive responses from his Twitter followers, with one fan telling him he was the "luckiest man in the world", to which he responded "too right!"
Mark then tweeted the exciting news that he had asked his brother Joshua to be best man at his and Michelle's wedding.
"I just OFFICIALLY asked my brother @Joshwright4 to be my best man!!" said Mark. "He will tell you the answer!!"
"I wish there was a stronger word than yes," replied Josh. "No need to even ask me @MarkWright_ so happy you are marrying @michkeegan she's a ledge love you both."
Bride-to-be Michelle then joined in the boys' conversation, tweeting "Awww!!! So happy!!! Get planning Joshy Boy! Love ya! 😘 xxx."
Mark and Michelle's love began in Dubai, after they fell for each other at a New Year's Eve party.
The couple have been inseparable ever since and Mark's manager even commented that the pair were always together when he posted a photo Michelle sitting on her partner's lap during a flight.
"On a plane," wrote Neil Dobias. "A seat each and they still have to be joint (sic) at the hip."
Mark, who proposed in October 2013, has previously spoken about how his relationship with 26-year-old Michelle transformed his life.
"I think everyone knows I wasn't the best boyfriend in the world before but this time it's for real," he said. "Two years ago I was reading FHM and now my girlfriend is the best-looking girl in FHM. I do really love her."