Firstly, men (Assuming you are such) do not have “brunch”. They have a late breakfast, or an early lunch.
Now that we’ve dealt with that, a few pointers from me;
Cafe Deco, Gloucester Road. Simply the finest espresso in that part of town, IMO. Not totally in the South Ken area, but very good place.
The big Corner Shop on Knightsbridge, especially the Georgian Terrace on the fourth floor, does a good spread. Even if you don’t see it on the menu, you can always order smoked salmon and scrambled eggs. Very good it is too.
There’s the Admiral Cod, on Mossop St. Always a good meal to be had there.
Sadly, the immediate area around South Ken has become a little anodyne of late, much like many commercial areas. Otherwise, I’d have said go to the now sadly departed Dinos.
Edit – *Hands over crisp virtual-fiver to Al 😉 *