What happens with lethargy when Haste is cast again on a creature before first cast runs out?

Haste states

When the spell ends, the target can’t move or take actions until after its next turn, as a wave of lethargy sweeps over it.

However, let’s say Character A cast Haste on Character B. In the 10th round (final round of haste if concentration not broken), Character B casts Haste on himself.

What happens during the next round?

  1. Do they lose a round of the “new” haste while they are lethargic and lose movement and actions?
  2. Does the new haste override the lethargy until it ends?
  3. Is it some combination? Retain AC/Dex modifications but lose actions/movement?
  4. None of the above?