Alongside a selfie with Dana and her four-year-old son Jasper from a previous relationship, Lachy wrote: 'On Thursday night, Dana asked me to marry her at home under a fairy light sky and a very excited little boy in a beautiful bow tie.'
The very happy trio can be seen standing at the end of a bed, with twinkling fairy lights draped across the room.
But, Dana revealed in her own gorgeous engagement post, that Lachy had already popped the questions weeks earlier!
'At the end of our summer holidays, I walked into the most beautiful surprise - a room filled with the most incredible flowers and Lachy singing at his piano and then asking me to marry him. It was such a surprise and so special. Our faces say it all,' she began.
'It was something very meaningful for us to both have the opportunity to propose to one another, each in our own way. Last week, with the most beautiful (and excited!) little boy by my side in a special bow tie, it was our time to ask Lachy our special question - and it was so, so wonderful.'
The Purple Wiggle went public with his new romance in October 2019 by posting a snap to Instagram.
At the time, it was a little over a year since he announced his shock split from his Emma, after just two years of marriage.
Lachlan and Emma both met Dana, 34, when the dancer filmed an episode of The Wiggles in December 2018.