Imogen Anthony has lashed out at her ex-boyfriend Kyle Sandilands in a cryptic Instagram post.

KIIS radio host Sandilands threw his girlfriend and communications director Tegan Kynaston a lavish 35th birthday bash at their multimillion dollar Woollahra home last week and soon after, Anthony posted critical comments.

"It's cowardly, hurtful … to be told that someone still 'loves you' and 'doesn't want it to be over' (that's right babe, you can see it all if you like) so the other person cannot move on," Anthony wrote.

Anthony, 28, announced her split from Sandilands, 49, last year after eight years together.

She said she was "miserable" during the relationship.

"I WAS miserable because I was left with a mess (and) he threw his responsibilities when it got too hard … I'm sick of covering for you, be a man," she wrote.

A rep for Sandilands declined to comment on Anthony's claims.

It comes after Kynaston, who began dating Sandilands not long after his split from Anthony, splashed happy snaps of her lavish birthday celebrations across social media.

On Friday night, Sandilands hosted a fancy birthday dinner with guests including his good friend Kings Cross identity John Ibrahim, his model girlfriend Sarah Budge, and convicted drug trafficker Simon Main.

The couple's Nueva sangria was flowing as guests were treated to live performers and an elaborate cake.

"Thirty-five - what a night! Thank you to everyone who celebrated with me. I'm so grateful for having so many amazing friends! And a special thank you to my great love who organised it all, I'm a very lucky girl," Kynaston gushed on Instagram.

Originally published as Imogen unleashes on ex Kyle