Yes, we're talking the other woman in his life - his mum! Because while you've probably already signed up your mum to help you choose your gown, pore over stationery details or even rustle up a cake, it's easy for his mum to be overlooked (after all, how often do you hear anyone talking about mother of the groom outfits?!).
The good news is that whilst, historically, this role has been more limited, these days there are no rules; your future mother-in-law can do as much (or as little) for your celebrations as you all feel happy with. To inspire you, here are some traditional duties - plus some fresh ideas to involve her in your day…
Liaise with the mother of the bride
It's a good idea for the mother of the groom to touch base with the mother of the bride to liaise about outfits. Your mum might feel strongly that she has first dibs on hot pink, for example - and traditionally the groom's mum should make sure she's not stepping on any fuchsia peep-toes! But even if you're not sticking to any formal etiquette, it's still wise for the mums to chat - after all, neither of them will want to turn up in matching frocks!
Host one of the gatherings
If your future mother-in-law likes to entertain, you could let her show off her hostess skills by throwing your engagement party or rehearsal dinner. She gets to shine and you get to relax!
It's customary for the groom's parents to help financially with certain aspects of the wedding, including bouquets and buttonholes - but in 2018, the only hard-and-fast rule is that any financial contributions are ones that you're all comfortable with.
Advise on the guest list
The mother of the groom will be worth her weight in gold when it comes to planning the guest list - who better to advise on which far-flung family members should be invited on his side, and to help coordinate and chase up the RSVPs? (Especially if your groom doesn't have a clue!)
Help plan and prepare for the big day
You can never have too many pairs of hands in the run-up to your wedding, and there'll be plenty of tasks for an enthusiastic mother of the groom. She has great taste in decor? Ask her to help style your tables. She's a whizz with all things crafty? Let her DIY your favours. You get the benefit of her skills, and she'll be thrilled you asked.
Attend the hen party
She might not want to stay drinking Prosecco until 3am, but it's a nice touch for the mother of the groom to be invited to - and attend - your hen night. Even if she only stays for an hour or two, it's the perfect way for her to meet and bond with your mum, your closest friends - and you!
Advise on the seating plan
Can your groom's Uncle Dave sit next to his Auntie Sue - or will the wedding cake be flying?! You might not know the answer - but you know a woman who does! With her insider info, your table plans will be a breeze!
Take part in the mother-and-son dance
Kick-start your disco with a mother-and-son dance! Whether the two of them hit the dancefloor at the same time as you and your dad, or have their own moment in the limelight, it's a lovely way to make a memory they'll both treasure forever.
Stand in the receiving line
If you're having a receiving line (either straight after the ceremony or at the entrance to your evening reception), then the mother of the groom should be included.