Both NewsChannel 8 and the Washington City Paper are reporting that D.C. Council Chair Vincent Gray will announce this week that he will run for mayor against Adrian Fenty.

Gray is expected to make his announcement shortly before 2 p.m. on Tuesday, the reports say.

The news means Mayor Fenty has his first serious challenger in September’s Democratic primary. It also means we can expect to see one or more senior D.C. Council members announce they will run for chair in the coming weeks. Early speculation in a possible chair’s race has included Ward 2’s Jack Evans and At-large member Kwame Brown.

We’ll have more on this major local politics development later on.