What does a man who marries his mistress create?

On occasions men marry their mistresses. The late Sir James Goldsmith on marrying his mistress Lady Annabel Birley declared "When one marries one's mistress, one creates a vacancy".

There is some dispute about the exact wording. quotesmith has it as "When a man marries his mistress it creates a job opportunity.", while highbeam research quoting National Review; 9/1/1997; Simon, John, (Goldsmith obituary) says this: "Women adored him and he adored women. He married three times and had numerous mistresses. (Yet another Jimmyism: 'When you marry your mistress you create a job vacancy.') He was loyal, in his own way, to all of them, and all of them were loyal to him. He had eight children by four different women, and never have I seen a more closely knit family."
https://en.wikipedia.org/wiki/Mistress_(lover)

Vacancy was what I was looking for all right BB, good answer. Didn't know who said it but sir JG sounds a lot of fun.

His daughter Jemima is about to marry Hugh Grant

An even BIGGER mess!

And before anyone says it, 'mistress' is not a variation of 'my stress'.....

...nor is it something between a mister and a mattress, but then again...