The shelter rule is a doctrine in the common law of property under which a grantee who has received an interest in property from a bona fide purchaser will also be protected as a bona fide purchaser, even if the grantee would not legally qualify for this status.
The grantee is "sheltered" from other claims by the grantor's status as an actual bona fide purchaser.
[1] This rule comes into play in situations under a number of circumstances.
For example, where a bad actor agrees to convey the same real property to multiple other parties.
However, under the shelter rule, Charles will receive the same treatment as Bob, and will prevail over Andrew in a legal contest over the ownership of Blackacre.