In it, Mr Bush told Mr Trump he would not be able to attend Friday's inauguration because, "my doctor says if I sit outside in January, it likely will put me six feet under.

"Same for Barbara," he added. "So I guess we're stuck in Texas."

Mr Bush said he would be with Mr Trump "in spirit", and wished him well as he assumed the presidency.

"If I can ever be of help, please let me know," he wrote.