My feeling is that where there is smoke there is fire. It's cropped up quite a bit in the last few weeks. Unless JC is imminently dying of something diagnosed, I can't imagine that his family wants or will have him back....including his wife.
It's a serious issue. JC has been wanting to came to Spain for months now that his court cases have been dismissed, it's creating a problem for the government and specially Felipe.
I have no doubt, like many others in Spain, JC has been putting feelers in the press to see the reaction about his return. Not long ago some friends were apparently saying "he wants to come back to Spain, to Zarzuela and with the same financial assignation he had before he left - over 150, 000 euros annually."
The problem is that there is no way he's going to return to Zarzuela - a palace intrinsically linked to the Head of State or will have the same financial assignation he had before 2020 when Felipe retired that assignation.
Moncloa, the govenment, says it's a matter for the Royal House. Felipe doesn't say anything but father or not, doesn't want JC in Zarzuela and with a public salary when the public opinion is so against him.
There are no many options open to JC if he wants to return. If Patrimonio Nacional (Royal National Heritage) gives him a place to live on tax payers money, it'll be a scandal. If he buys something as a private person, he will have the worst of the reality shows "journalists" continiously asking scandalous questions day in and day out.
By law, if there are no longer court cases against him, he can return. But this is no longer about law and its loopholes, he's been convicted by public opinion and Felipe has to be very careful because the government is leaving the decision about his father up to him.
The best thing JC can do is to stay away from Spain. Maybe try to live in a country like Portugal where many of his young roots are and make private trips to Spain. I just don't see him living permanently in the country. It'll be a poison chalice for Felipe.