How would you make the last name Watts possessive?

There are two accepted forms for possessive singular nouns that end with an s:

Add an apostrophe (') after the existing s at the end of the Word:

• Watts'

Add an apostrophe s ('s) after the existing s at the end of the Word:

• Watts's

Example:

The meeting is in Mr. Watts' office.

The meeting is in Mr. Watts's office.