Defending champion Highland Reel is in line to become only the third horse to win back-to-back King George VI and Queen Elizabeth Stakes, weather permitting.

Rain is forecast in the lead-up to Saturday's Group One feature at Ascot and the stable admits it is a concern.

"We are very mindful of the weather, I must admit," Coolmore's UK representative Kevin Buckley said:

"Talking to Aidan (O'Brien) this morning it is likely we will have two runners and they will be the full-brothers Idaho and Highland Reel.

"Highland Reel likes Ascot. He does prefer good or better ground and I must point that out.

"Whether we can say Idaho is good as his brother, it is hard to say as he not won a Group One yet, let's not forget, whereas Highland Reel has won six in three different continents. It's a hard act to follow, but he is clipping at his heels.".

"Highland Reel likes Ascot. He does prefer good or better ground and I must point that out. He is tough and durable and gives his all every time."

The King George received a significant potential boost over the weekend after connections of dual Oaks heroine Enable gave the filly the option of taking on the males for the first time.

Trainer John Gosden is expected to announce on Wednesday (Thursday AEST) whether she will run.