Circles in a square and diameter of the circle

[Wilmer]

A circle is inscribed in a square with sides = 40.

A smaller (of course!) circle tangent to the above
circle and 2 sides of the square is inscribed in
one of the corners of the square.

What is the diameter of this circle?

 

[Olinguito]

Spoiler

$20(\sqrt2-1)$, easy.

 

[Wilmer]

No.

Spoiler

diameter = 40(3-2√2) = ~6.86

Not as easy as it appears...

 

[Olinguito]

Spoiler

You’re right. I overlooked the teeny bit in the extreme corner.