Well, it happened sometime after 1652:

https://www.dsl.ac.uk/entry/dost/surreptitiously

Also in the time-honored way of English, we didn't really standardize spelling for another 200 years. Then we started being really pedantic.

And (Norman) French was the official legal language of England from 1066 to 1362, at a time it wasn't even the official language of France itself (that only happened in 1539 with the ordinance of Villers-Cotteret replacing Latin in legal documents).

To this day some ceremonials of Parliament like the King's Assent to promulgate legislation are still in Norman French.