Peyton Manning has always been class personified, so this story is not shocking at all.
Manning got an invitation to a wedding from Anna (Anne?) and James, who I would assume are huge Broncos or Manning fans.
The person who shard the photo said her sister had sent the invitation to Manning and his reply is classic. Manning of course had to regretfully decline because of football obligations, but he did sign and autograph the invitation.
H/T Reddit