However, the former Liverpool, Inter and Real Madrid boss stayed on and revitalised the club in the Championship.
He leaves having spent three full seasons with the club in which he oversaw their promotion back to the Premier League and re-established them as a top-flight club.
In his tweet, Ornstein wrote: "The news many Newcastle fans were dreading - Rafael Benitez to leave after three years as manager".
Newcastle will now kick off the search for a new manager and Grant may be part of the picture as it is claimed the Magpies are considering him for an unspecified role at St. James' Park.
"We would also like to thank our supporters, players and staff for their patience during a period of uncertainty", read the club's 136-word statement on the matter.
The Magpies had hoped to come to an agreement with their manager before his contract had expired, but it is believed Benitez failed to agree fresh terms with owner Mike Ashley.
It has meant that - the £20million acquisition of Miguel Almiron aside - Benitez was left working with scraps.
There is certainly experience with Steve Bruce who has also managed in the Premier League but in comparison to Benitez's proven track record in the top flight of English football it is less than favourable.
With names such as Gennaro Gattuso, Garry Monk and Mikel Arteta being thrown around by betting companies as the potential next man in charge, it could be summer plans are scrapped entirely depending on the approach Benitez's successor wants to take.
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