Great guess, Monzo are partnering with TransferWise & you will be able to use the integration in Monzo’s app -
when Tom mentioned this at the open office, he said that this would be available when the current accounts launch so I assume (hope) that it will be ready straight away.
Based on Monzo’s past record with fees, I expect you’ll only pay TransferWise’s fees. But I could be wrong.
PS - If you’re wondering about any of the other new functionality for the current accounts, it’s listed here -