The latest run of the BBC One drama sees charismatic Michael take over as the school's headmaster, having been appointed by the education authority to turn its fortunes around.
A number of other new recruits also join the school in the opening episodes - including deputy head Sian Diamond and Head of English Linda Radleigh, who are not strangers to Michael.
"Michael's had relationships with both Sian and Linda," Newman told TV Choice. "The one with Sian was by far the most serious of the two and, although he ended it, he still has feelings for her."
Sian, played by former Holby City star Jaye Jacobs, works at the school with new husband Jez (Alex Walkinshaw) - but has been tipped to start questioning her marriage when she comes face-to-face with Michael again.
Jacobs told the magazine: "Sian fell in love with Jez's cheeky, chirpy character. He brings out her fun-loving side, but she's a Cambridge graduate and Michael offers her the intellectual stimulation that Jez never could."
Waterloo Road returns on Wednesday at 7.30pm on BBC One.
> Waterloo Road spoiler: The school's new headteacher arrives
> Waterloo Road spoiler: Jez and Sian receive some shocks
> Waterloo Road spoiler: Grantly is furious over a new arrival
> Read all the latest Waterloo Road news