The couple of 11 years called time on their six-month marriage back in April and subsequent reports have claimed that Quinn dumped Klass on her 34th birthday, though he has denied this "ridiculous" suggestion.
Despite the break-up, Klass and Quinn have both committed to attending the nuptials of their close friends next month.
"They've both got reason to be there," a source told The Sun.
"Graham is an usher, but then Myleene has grown close to Rochelle over the years. The feeling is why should she give up her invite when she's done nothing wrong? She doesn't see why she should shy away from it."
"Myleene confided in Rochelle and promised she'd still be there on her wedding day. She said she will stay strong and keep it together. Her upset has turned to anger."
Another insider told The Mirror that Klass's loved ones have warned her off attending the ceremony so soon after her separation.
"Pals are encouraging Myleene not to attend," they said. "It's not the most pressing concern on her mind, understandably. But obviously, if they both do go, it could make things really awkward."
Humes and Wiseman will reportedly marry at Blenheim Palace in Oxfordshire, which is the birthplace of Winston Churchill.