The couple, who married in 2015, are already parents to sons Teddy and Kit.
Although Jermaine and Ronan have joined the programme, BBC bosses have said ‘no decision has been made on the cover for [Alex’s] maternity leave’.
On Jermaine and Ronan joining, The One Show editor Rob Unsworth said: ‘We’re thrilled to have Ronan and Jermaine join us as the regular One Show hosts alongside Alex on the sofa.
‘It’s an exciting new chapter for the show, and we’re looking forward to viewers vetting to know a different side to such well-known faces.’
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