A key for the doors of an 11th century tower has been anonymously returned - almost 50 years after it disappeared.
The brass key for St Leonard's Tower was posted to English Heritage's head office, along with an anonymous note apologising for the delay in its return, explaining that it had been "borrowed".
It still fits inside the locks of the doors to the Norman tower in Kent, which was built between 1077 and 1108, although it no longer rotates to unlock them.
After the key's mystery disappearance, the locks were replaced in the structure.
According to English Heritage, the key is thought to be around 100 years old.
In the "tantalising note", which was delivered with the key, the mystery person wrote: "Borrowed 1973. Returned 2020.
"Sorry for the delay. Regards."
Speaking to Sky News, Samantha Stones, properties curator at English Heritage, said: "This is not the sort of thing that happens every day.
"We would really love to get in touch with the anonymous returner... so we can thank them properly and hear a little bit more about the story behind the disappearance."
English Heritage says it wants to reward the person who returned the key with a "gift of membership" to the organisation.
The tower, which is now a "well-preserved" ruin, is thought to have been built as an administrative building by the Bishop of Rochester shortly after the Norman invasion in Hastings - but little is actually truly known about the structure's purpose.
Others believe that it was built by Bishop Odo of Bayeux - the half-brother of the then king, William the Conqueror, as part of a castle.
English Heritage is asking the sender of the note to get in touch with its Customer Services team on 0370 333 1181 or email customers@english-heritage.org.uk.
