The 19 year-old will be there for Anne Cox as she weds long-term partner Robin Twist - who helped raise Harry after his parents split when he was seven.
Harry’s One Direction bandmates Louis, 21, Zayn, 20 Liam, 19, and Niall, also 19 are thought to be attending the wedding which Harry’s mum reportedly scheduled around the band’s tour dates.
Guests will only be told details of the wedding at the last minute to keep the venue under wraps.
Anne, 43, who lives in Cheshire, with Robin and daughter Gemma, 20, has always supported the singer’s ambitions… and his love life!
She once said about her lothario son: ‘He’ll make a very nice boyfriend when he’s ready. He’s very romantic but doesn’t want to tie himself down at the moment.
‘Harry is obviously very handsome or ‘fit’ as the girls would say. Whoever Harry falls in love with in the future will be a really lucky girl.’
And mummy’s boy Harry has described his mum as one of his best friends, admitting she is the only one who really knows what’s going on in his infamous personal life: ‘I tell her everything, and she knows the truth.’
The singer took Anne to this year’s BRIT Awards as his date.
Harry is not the only member of One Direction to take on the role of 'best man'. Niall Horan recently put his band commitments on hold to stand at his brother Greg's side at the altar as his best man in March.
1D fans flocked to the Irish wedding to catch a glimpse of Niall, who made sure he greeted many of them in person. The notorious ‘one-directioners’ will no doubt do the same at Harry’s mum’s big day