The Bid You Fear to Hear

You hold: ♠T632  ♥AKQJ6  ♦—  ♣KT83

Your auction begins as follows:

Would you bid 4♦ at this stage?  Or, do you believe you are too strong for 4♦ and/or you are uncertain that partner would take that call as a splinter in support of spades?

At the table, I bid 2♣ at this stage, artificial, fourth suit game forcing.

I chose to call 5♣ now.  My plan was to bid slam if partner DID NOT control bid 5♦, and to signoff in 5♠ if he did.

I am not sure if my plan was the best, but it worked out fine.  Partner did control bid 5♦ (the bid I fear to hear) over my 5♣ call and I followed plan by signing off in 5♠:

Now had his ♦K morphed into the ♠K, pard would have bid 5♠ over my 5♣ and I would have bid 6♠ .  Pard would have made that contract, too.