Hilton HHonors members (free to join for anyone, here) have to date benefited from a “spouse stays free” offer. This is obviously useful for those reasonably rare hotels where double occupancy is more expensive than single occupancy.
Whenever I was searching for Hilton hotel rooms, I’d always search for a price based on one adult staying, even when my wife was coming along. While she was never asked to prove she was my spouse when we have benefited from this offer, the terms very clearly limited the offer to a spouse (dictionary definition being “husband or wife”) . The good news is this has been substantially widened to the “second guest”.
So, whether it’s your honeymoon or you’re staying in a twin room with a colleague, you’ll only have to pay for single occupancy.