There’s a long tradition in diplomatic history of monarchs letting deposed monarchs from hostile countries live in their state in luxury. At worst it’s a lingering thumb in the eye of the country that has to continually acknowledge that there’s a deposed king who is living it up abroad whom their government cannot touch. At best it sets up a bud to re-take the throne at some future point, with the deposed king now completely loyal and beholden to the foreign king and his government.