With the 33-year-old set to tie the knot with Meghan Markle on May 19... or for those counting at home, in 121 days.
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On Wednesday, Prince William was chatting to British radio host Roman Kemp as part of a group discussion at the Campaign Against Living Miserably (CALM).
The DJ bravely prodded about the impending royal wedding... And more importantly - the role he'll be playing.
Laughing, Prince William confessed, "He hasn't asked me yet, just to clear that up. It could be a sensitive subject."
Despite not having the top job, Wills still considers himself as Harry's best man.
The proud dad is helping the charity with their latest venture the "Best Man Project" – which helps to celebrate men's friendships.
The 35-year-old confessed he's very close to Harry.
Wills explained their bond is like no other because of the experiences they've gone through, including the heartbreak they both suffered following the passing of their mother Princess Diana, back in 1997.
"Our relationship is closer than it's been because of the situation we've been through."
"Losing our mother at a young age it's helped us travel through that difficult patch together. You're like-minded. You go through similar things, it's a bond and it's something you know you've tackled together and come out better for it."
Wills clearly adores his "best mate."
"That's the thing about being a best mate, inevitable one of you is sometimes on an up while the other is on a down. You're always there for each other and repaying that favour."
And Duchess Catherine's hubby hopes he can be there for kids in a similar way.
In fact, William wants to help fathers and sons break down their barriers and be able to talk to one another.
"We've got to break that down where it's OK to talk. Sons, fathers, it's OK to have that chat. Someone's got to be the brave one and take the first step."
Who will Prince Harry pick to be his best man?
While Harry is yet to ask William to take on the top job, technically British Royal Weddings don't even have a best man in the proceeding!
British and European royalty expert Marlene Koenig explained to Town & Country, "The best man or best men are officially called supporters."
"William will probably be Harry's supporter."
In fact, Wills broke royal protocol for his 2011 nuptials to Kate Middleton, when getting Harry to step up for the role.
It is very likely that Harry will follow his brother's lead.
"Harry has several close guy friends, but there's no way he would ask anyone but William to take on the top job," one pal told Us Weekly.
For William's wedding, Harry took his responsibility very seriously, meticulously planning his big brother's stag party a month before the big day.
"While details are scarce, Will's office confirmed that the Prince's party took place in late March (about a month before the wedding)," Brides.com revealed.
"Hosted by his brother, Prince Harry, at a country estate, the party included Will's close friends James Meade, Thomas van Straubenzee, and Guy Pelly."
One thing is certain, William is overjoyed that his little brother has found love.
"We're very excited, delighted for them both," he said after Harry announced he was engaged.
"We're wishing them all the happiness at this very exciting time."
Joking, he added, "Personally, I hope it means he stays out of my fridge and will stop scrounging all my food, which he's done for the last few years."