'One or two more weeks left for Lily and I?' Jett asked in the caption.
And his mum was the first to reply, writing: 'Two decades?' followed by several heart emojis.
Former Biggest Loser star Michelle Bridges also weighed in on the couples' chemistry, writing: 'What!? Like we didn’t already have our invites to the euro wedding, and names down for the first and second born.'
Fans were also quick to comment.
'You two are amazing together, both on and off the dance floor!' said one follower.
'One or two weeks of dancing left maybe, but surely it’s a life time together - when are you guys going to come out and confirm it?!' another user wrote.