The 41-year-old star had not been in contact with the music mogul since they appeared together as judges on the UK version of 'The X Factor' - which Dannii left in 2010 - and since revelations of a relationship between the two were published in author Tom Bower's biography on Simon.
After signing up for a judging role on the Australian version of the show, however, Dannii received an unexpected call from Simon to find out which category she was mentoring.
In an interview with the new UK issue of Grazia magazine, Dannii revealed: ''I've not spoken to him since I left the show, yet he chose to film that moment. I really wish you guys could see it. Simon has some balls doing that. I find it bizarre that he's never been involved in the Australian version of the show before and then I'm on it and suddenly he wants to break the news as to what group I have.''
Dannii - who will soon be back on UK TV screens in 'Britain & Ireland's Next Top Model' - has also revealed she wants to have another baby.
The brunette beauty thinks it would be lovely for her two-year-old son Ethan to have a younger sibling but she needs to find a man first.
Dannii - who has been single since splitting from Ethan's father Kris Smith in April 2012 - said: ''I think I want another. But I can't just click my heels together and make it happen. I keep wondering how the hell I do it. Once Ethan got to two he started doing the most adorable things and I was like, 'Damn, I want another one.'
''All my gay friends have been asking if my ovaries are available for rent - they're close to running after me with a turkey baster!''