Hari Singh is a non-canonical character, created for the 2022 miniseries Why Didn't They Ask Evans?, an adaptation of the Agatha Christie novel of the same name. He is the butler of Lord and Lady Marcham.
In the first episode, Hari's salute to Bobby in naval style makes Bobby realize that Roger Bassington-ffrench, whose salute was just like that, had been in the navy as well.
In the second episode, Hari is assigned by Frankie (who has since taken up residence with the Bassington-ffrenches) to find Bobby at the garage in London and give him the driver's uniform that Frankie has stolen from the family driver. Hari finds a beaten-up Knocker instead (courtesy of Mr Angel), takes him to the hospital then heads over to Anglers' Arms and recounts all to Bobby.
In the third episode, he is among the guests at Bobby and Frankie's wedding.