Just in case, these are the effects of both cards, from wikia:
Neither player can add cards from their Deck to their hand except by drawing them. During either player's turn, when your opponent would Special Summon a monster: You can send this face-up card to the Graveyard; negate the Special Summon, and if you do, destroy it.
When a Spell, Trap, Spell/Trap effect, or Effect Monster's effect is activated that destroys a card(s) on the field: You can Tribute this card; negate the activation and destroy it. During the End Phase, if this card negated an effect this way during this turn: You can Special Summon this card from your Graveyard.
I know Thunder King can negate Stardust's summon without any response from it. However, what if Stardust is already on the field, properly summoned, and so is Thunder King, then I try to xyz summon Gem-Knight Pearl, for example, and my opponent says he'll negate the xyz summon? Can I tribute Stardust Dragon to negate Thunder King's effect?
Stardust's effect says it can negate any effect that would destroy a monster, and Thunder King's effect says so, but can I really negate it?